Whenever I try to add or edit and save a product on Magento 2.2.5, I get the error "A technical problem with the server created an error. Try again to continue what you were doing. If the problem persists, try again later."
I've tried everything listed in this thread: https://github.com/magento/magento2/issues/10071
I've also tried looking for error logs, but I can't find any errors at all relating to this problem, only a 500 response code for the Ajax save request.
I was able to add products fine before I used the Magento Migration Tool, which was a little while ago, but I don't recall making any changes that would affect this, nor do I remember installing any other extensions since using the tool.
I've been Googling this all afternoon and I've found multiple answers on Stack Exchange, none of which help me. I've tried changing the admin password, creating a new admin user and making sure I've got full admin permissions. I've also tried re-indexing, clearing the cache, recompiling and manually deleting the cache files.
My closest guess so far is that the migration tool made some changes in the database that is causing it to error on trying to add a new product, although I'd expect to see an error for this. I also haven't found any other errors, so if it is this it's not a fundamental issue and obviously just not migrating the data isn't an option.