Firmware is OK.
Sorry guys for wasting your time, but an accumulation of very unlikely factors led me to think that the culprit was the GPU firmware.
To make a long story short the culprit was a swap device I created on a NVMe hard drive around the same dates I started having problems. The strange thing is that the hard drive is fine and my system also crashed when I deactivated that swap partition, but maybe due to the summer heat I had some kind of data/memory corruption.
I can confirm that the firmware is totally fine. I'll close this thread now.
Edited by X6B