HTTPS redirects back to HTTP sometimes

Hello there!

Weird issue happens, need help :frowning:
i have url:
https://mysite.com/sslTest?bbb=&eeee=1

In some like random moments if i hit enter on browser url bar it redirects to HTTP:
http://mysite.com/sslTest?bbb=&eeee=1

I m using chrom

here is my htacces:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteCond %{REQUEST_URI} !/$
RewriteRule (.*) $1\.php [L]

ErrorDocument 404 https://mysite.com/404.php

Options -Indexes

Everything worked all the time and nothing seems to be changed to affect that :man_shrugging:
Also interesting fact is if i remove query it redirects back to page and HTTPS

I tried to add:

RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

What could be a problem?
Page returns error 400