All pages 302/502 bad gateway (nothing in logs, Magento 2.4.2)

Question

I am getting 502 bad gateway error showing in the browser for all pages, including admin. There is nothing in the logs of phpfpm (system/debug/exception).

In the nginx logs I am seeing the request as getting response 302, but with no additional error.

Background: I am trying to switch theme. I think I made a mistake by deleting the old theme from code before switching in the dashboard. I have done UPDATE theme SET type=0 in mysql.

I have made sure that all permissions are ok:

rm -rf var/cache
find var generated pub/static pub/media app/etc -type f -exec chmod g+w {} + &&
find var generated pub/static pub/media app/etc -type d -exec chmod g+ws {} + &&
chown -R :www-data * &&
chmod 777 -R var generated pub 

Health check is 200 ok. phpfpm access log also register the request as 302, but with no reason added to it:

10.1.2.3 -  24/Sep/2021:10:22:23 +0000 "GET /health_check.php" 200
10.1.2.3 -  24/Sep/2021:10:22:33 +0000 "GET /health_check.php" 200
10.1.2.3 -  24/Sep/2021:10:22:39 +0000 "GET /index.php" 302
10.1.2.3 -  24/Sep/2021:10:22:43 +0000 "GET /health_check.php" 200
10.1.2.3 -  24/Sep/2021:10:22:53 +0000 "GET /health_check.php" 200

How can I debug this further?

UPDATE

I tried changing the nginx parameters, but it doesn't help. I am currently trying to debug with adding outputs within magento code (based on this article)

This is what I see when I go to /admin page:

#1 Magento\Backend\Model\View\Result\Redirect\Interceptor[Magento\Framework\Controller\Result\Redirect]#0000000042b6bde00000000057bd9cbd#->setPath() called at [vendor/magento/module-backend/Controller/Adminhtml/Auth/Login.php:70]
#2 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor[Magento\Backend\Controller\Adminhtml\Auth\Login]#0000000042b6bc3f0000000057bd9cbd#->getRedirect() called at [vendor/magento/module-backend/Controller/Adminhtml/Auth/Login.php:55]
#3 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor[Magento\Backend\Controller\Adminhtml\Auth\Login]#0000000042b6bc3f0000000057bd9cbd#->execute() called at [vendor/magento/framework/Interception/Interceptor.php:58]
#4 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->___callParent() called at [vendor/magento/framework/Interception/Interceptor.php:138]
#5 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->Magento\Framework\Interception\{closure}() called at [vendor/magento/framework/App/Action/Plugin/ActionFlagNoDispatchPlugin.php:51]
#6 Magento\Framework\App\Action\Plugin\ActionFlagNoDispatchPlugin#0000000042b6bc0e0000000057bd9cbd#->aroundExecute() called at [vendor/magento/framework/Interception/Interceptor.php:135]
#7 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->Magento\Framework\Interception\{closure}() called at [vendor/magento/framework/Interception/Interceptor.php:153]
#8 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->___callPlugins() called at [generated/code/Magento/Backend/Controller/Adminhtml/Auth/Login/Interceptor.php:23]
#9 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->execute() called at [vendor/magento/framework/App/Action/Action.php:111]
#10 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor[Magento\Framework\App\Action\Action]#0000000042b6bc3f0000000057bd9cbd#->dispatch() called at [vendor/magento/module-backend/App/AbstractAction.php:151]
#11 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor[Magento\Backend\App\AbstractAction]#0000000042b6bc3f0000000057bd9cbd#->dispatch() called at [vendor/magento/framework/Interception/Interceptor.php:58]
#12 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->___callParent() called at [vendor/magento/framework/Interception/Interceptor.php:138]
#13 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->Magento\Framework\Interception\{closure}() called at [vendor/magento/module-backend/App/Action/Plugin/Authentication.php:143]
#14 Magento\Backend\App\Action\Plugin\Authentication#0000000042b6bcd40000000057bd9cbd#->aroundDispatch() called at [vendor/magento/framework/Interception/Interceptor.php:135]
#15 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->Magento\Framework\Interception\{closure}() called at [vendor/magento/framework/Interception/Interceptor.php:153]
#16 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->___callPlugins() called at [generated/code/Magento/Backend/Controller/Adminhtml/Auth/Login/Interceptor.php:32]
#17 Magento\Backend\Controller\Adminhtml\Auth\Login\Interceptor#0000000042b6bc3f0000000057bd9cbd#->dispatch() called at [vendor/magento/framework/App/FrontController.php:186]
#18 Magento\Framework\App\FrontController\Interceptor[Magento\Framework\App\FrontController]#0000000042b6bf830000000057bd9cbd#->processRequest() called at [vendor/magento/framework/App/FrontController.php:118]
#19 Magento\Framework\App\FrontController\Interceptor[Magento\Framework\App\FrontController]#0000000042b6bf830000000057bd9cbd#->dispatch() called at [vendor/magento/framework/Interception/Interceptor.php:58]
#20 Magento\Framework\App\FrontController\Interceptor#0000000042b6bf830000000057bd9cbd#->___callParent() called at [vendor/magento/framework/Interception/Interceptor.php:138]
#21 Magento\Framework\App\FrontController\Interceptor#0000000042b6bf830000000057bd9cbd#->Magento\Framework\Interception\{closure}() called at [vendor/magento/framework/Interception/Interceptor.php:153]
#22 Magento\Framework\App\FrontController\Interceptor#0000000042b6bf830000000057bd9cbd#->___callPlugins() called at [generated/code/Magento/Framework/App/FrontController/Interceptor.php:23]
#23 Magento\Framework\App\FrontController\Interceptor#0000000042b6bf830000000057bd9cbd#->dispatch() called at [vendor/magento/framework/App/Http.php:116]
#24 Magento\Framework\App\Http\Interceptor[Magento\Framework\App\Http]#0000000042b6be250000000057bd9cbd#->launch() called at [vendor/magento/framework/App/Bootstrap.php:263]
#25 Magento\Framework\App\Bootstrap#0000000042b6bea40000000057bd9cbd#->run() called at [pub/index.php:29]

string(122) "http://example.com/index.php/admin/admin/index/index/key/d4e355fa9340a85b70a3074a25985590af30eb5e5829e53436cd1ffae5b8102c/"

#1 Magento\Framework\App\Response\Http\Interceptor[Magento\Framework\HTTP\PhpEnvironment\Response]#0000000042b6be230000000057bd9cbd#->setRedirect() called at [vendor/magento/framework/Controller/Result/Redirect.php:114]
#2 Magento\Backend\Model\View\Result\Redirect\Interceptor[Magento\Framework\Controller\Result\Redirect]#0000000042b6bde00000000057bd9cbd#->render() called at [vendor/magento/module-backend/Model/View/Result/Redirect.php:67]
#3 Magento\Backend\Model\View\Result\Redirect\Interceptor[Magento\Backend\Model\View\Result\Redirect]#0000000042b6bde00000000057bd9cbd#->render() called at [vendor/magento/framework/Controller/AbstractResult.php:125]
#4 Magento\Backend\Model\View\Result\Redirect\Interceptor[Magento\Framework\Controller\AbstractResult]#0000000042b6bde00000000057bd9cbd#->renderResult() called at [generated/code/Magento/Backend/Model/View/Result/Redirect/Interceptor.php:23]
#5 Magento\Backend\Model\View\Result\Redirect\Interceptor#0000000042b6bde00000000057bd9cbd#->renderResult() called at [vendor/magento/framework/App/Http.php:120]
#6 Magento\Framework\App\Http\Interceptor[Magento\Framework\App\Http]#0000000042b6be250000000057bd9cbd#->launch() called at [vendor/magento/framework/App/Bootstrap.php:263]
#7 Magento\Framework\App\Bootstrap#0000000042b6bea40000000057bd9cbd#->run() called at [pub/index.php:29]