CDbConnection failed to open the DB connection after cache clear


I started to have issues with my Mailwizz. At some point, I was no longer able to even create and test a campaign. I would get Error 400 every time I would try to set up a campaign. Here's the screenshot of the error:

Then, I went to the backend to check the delivery logs and ran into another error, now 500 this time. Here's the screenshot:

I did some research and found here the suggestion to clear the cache. I went to var/www/mymailwizz/apps/common/runtime/cache and ran rm on all files. Then, I rebooted the server and after some time went to my mailwizz page only to find out that it's no longer working.

Then, I went to the server and enabled debugging in apps/init.php.

Upon my check, I've got a page with errors detailed in my followup reply in this thread.
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And, if this is of any help, here are the specifications of the server:

CPU: Intel Xeon E3-1270v6 - 4c/8t - 3.8GHz /4.2GHz
RAM: 32GB DDR4 ECC 2400 MHz
500 GB of storage space
Control Panel
Root access to the server
Access via the KVM/IP graphic console
Anti-DDoS Pro included

Here's current disk space on the server:

Found a fix on my own. The issue was that the space on the partition where mailwizz is placed was out of space.

My campaigns are giving error (Errcode: 28 "No space left on device")

I reduced Delivery servers logs removal days * from 180 to 60 days, in order to clear older logs.

But nothing happened in 1 hour. After how much time the CRON will run ? Else how to make it run manually ?