Reinstall prompt but nor trying to reinstall

Nextcloud version: 14 (?)
Ubuntu 16.04
Apache 2.4.16
PHP version: 7.2.22

The issue you are facing:
It started like this. But after repopulating the config.php i get a Internal Server Error.

Running cloud for more than a year, stopped working with reinstallation prompt, config.php empty (no backup of config, but of data)

Is this the first time you’ve seen this error?: Yes

Steps to replicate it:

Apache2 errorlog:

[Fri Sep 13 19:43:11.407180 2019] [php7:error] [pid 30587] [client 212.*.*.*:37276]
PHP Fatal error:  
Uncaught Error: 
Class 'RedisCluster' not found in /var/www/cloud/config/config.php:1173\nStack trace:
#0 /var/www/cloud/lib/private/Config.php(214): include()
#1 /var/www/cloud/lib/private/Config.php(63): OC\\Config->readData()
#2 /var/www/cloud/lib/base.php(140): OC\\Config->__construct('/var/www/cloud/...')
#3 /var/www/cloud/lib/base.php(577): OC::initPaths()
#4 /var/www/cloud/lib/base.php(1056): OC::init()
#5 /var/www/cloud/index.php(40): require_once('/var/www/cloud/...')
#6 {main}\n  thrown in /var/www/cloud/config/config.php on line 1173

Not sure what to do with that. Any hints on how to resolve this?
Thanks alot!