XPS 15 9550 CPU still throttles!

Greetings,

I thought all my problems with CPU capping/throttling were gone with the BIOS update, but it seems they are not. 

I "had" a problem where on battery power my CPU would throttle to ~0.8GHz when playing games. In the menu the CPU would still be around 2.9GHz, but the moment the actual game would start, the CPU would throttle to 0.8GHz and my FPS would drop drastically. I tried numerous solutions to solve it, but since I mostly play games on AC, and in all other situations CPU would function normally (AC like frequencies), I decided to let it be.

But, since yesterday, my CPU is capped to 0.8GHz whether I'm on battery or on AC. Nothing I do can change it. I tried switching power profiles, setting the minimum processor state to 90% and 100%, changing the thermal settings in Dell Power Manager, reverting Windows to previous states where I know it worked normally, resetting the BIOS, nothing helped - the CPU is still capped at 0.8GHz. 
I thoroughly looked into it and it seems the reason for throttling is BD PROCHOT. It appears it sends CPU to its lowest power state, as if it was overheating. The CPU is definitely not overheating, temperatures are around 35°C and it's idling. 

For the first issue (gaming performance drop) I have no idea what was the cause, but the second I suspect has to do with firmware update for Thunderbolt (Intel_TBT3_FW_UPDATE_NVM16_A03_02.12.07.exe). Because it is the only thing that changed in the time.
I have the FHD, i5 version with BIOS 1.1.19.

Please help, this is making my XPS basically unusable...