Why does Symfony start to slow down when calling the handleRequest method on a Form in dev/test env, and after reinstalling the server it starts to slow down again?

Question

symfony

Over time, in a dev or test environment, when using the handleRequest() method of the FormInterface component on Symfony (5.1+), some abnormally long brakes occur during the execution of a POST request - the request starts to execute up to 20 seconds. When you change the environment to prod - instantly.

When installing a project (git clone) on another server, or deleting and reinstalling a virtual machine (WSL, Vagrant), the same code in the dev or test environment again starts working quickly and without delay, and then, after a while, such Problems.

Deleting the var folder doesn't help, neither does a complete deletion and a new clone of the repository. Only complete demolition and reinstallation of the virtual machine helps (Ubuntu 20.04, ngnix, php7.4).

Has anyone come across? Can I somehow cure it without demolishing the entire virtual machine?