500 Internal Server Error after update to 1.6

Hi. I have error 500 Internal Server Error after update to 1.6.
What could be the problem?

(500 return only modular pages)

On version 1.5.8 everything works well (200 OK)

https://learn.getgrav.org/16/troubleshooting/internal-server-error

Grav 1.6 needs PHP 7.1.3..or higher
https://learn.getgrav.org/16/basics/requirements

All this was done. It's not working. I had to return the old 1.5.8 version.

I had it too.
I was not sure it was because of the Grav upgrade, since my website was working fine for a while (haven't tested everything though). So I started to troubleshoot nginx and apparently it was because of some PID stuff. Something similar to this:
https://www.digitalocean.com/community/questions/unable-to-start-nginx-failed-to-read-pid-from-file-run-nginx-pid

But I didn't manage to fix it, so I restored my server backup. 500 was gone, but when I updated Grav again, I started to get other errors (not server, but Grav errors this time). So at the end it was a mixture of updating to Grav 1.6.6, updating all plugins etc. and it somehow worked at the end.

I just updated to 1.6.8 and get 500 internal server error. Everything worked before the update. PHP version 7.2. Uncommented the Rewritebase in .htaccess as suggested but no change. The admin pages work fine. So far every update has broken my site and I have had to reinstall everything. Maybe Grav just isn't for me ...