I have Magento 2.2.6 version. After signin, customer name is not showing on top dropdown bar, however if I reload the page aur goto another page it then appears. Another issue is that when adding products to cart, first time the product is shown, after that if I add another product to cart then the mini cart shows "No products", however going to checkout/cart page, products appear there. It seems they are just not shown in mini-cart. The issue appear to be in incognito mode. I have fpc enabled, and using varnish.
We had the same issue in the same 2.2.6 version, fixed it with this patch: https://github.com/magento/magento2/pull/14973
If you open the link adding .patch to github's url you'll get it in a patch format: https://github.com/magento/magento2/pull/14973.patch
Debugged it. It was my theme issue. Upgraded the theme and it was resolved.