Page rendering is completely broken

Nextcloud page rendering is completely broken (It looks something as follows)

It was fine before update to 18.0.7

I’ve following 2 messages in Admin -> Logging

Error	cssresourceloader	Could not find resource css/server.css to load	
Warning	core	Failed to compile and/or save /var/www/nextcloud/core/css/server.scss	

I do see /var/www/nextcloud/core/css/server.scss, however I don’t see server.css.

What is causing this? (Themes are already disabled)

Following steps seem to resolve the issue:

sudo -u www-data php occ maintenance:mode --on
sudo redis-cli -s /var/run/redis/redis.sock
flushall (OK was response)
sudo -u www-data php occ maintenance:mode --off
sudo -u www-data php occ files:scan --all