API encryption key issue

I run them in windows with apache.

There is your reason. But it might be bunch of other stuff.

Go through the log files and see if you can find some reproducible steps for that error. Write test that proves that the error exists. Fix the error and test should become green.

Before using Laravel's encrypter, you must set a key option in your config/app.php configuration file. You should use the php artisan key:generate command to generate this key"

You can find the generated application key(APP_KEY) in the .env file.

The app_key and cipher are present in config and env file. As I said the error happens only with a few requests and I don't know a way to test it.

Do you use OPcache https://www.php.net/manual/en/book.opcache.php if so try to disable it.

I've noticed this problem a long time ago

No, I don't have opcache enabled.