FastCGI cache issue on form submission

PHP was recently upgraded to 7.2 FastCGI. To update my custom php application I had to switch to MySQLi. Everything else seems to work. However, we had the issue that form submissions (changes to the database) didn’t show up on the webpage until a shift reload. Tried a few changes with opcache to see if it solves the issue but it didn’t. Switching to 7.2 CGI seems to solve the problem. Any thoughts what could be the reason for that?
Thanks,

Gunter