Sigma 20mm f1.4 broken aperture mechanism

[lukash]

I bought an used Sigma 20mm f1.4 DG art for cheap and it's definitely the sharpest lens I own. The main problem with it is that the lens doesn't really go beyond f2 or f2.8 when taking photos. With videos I can go all the way to f16. The aperture motor doesn't spin enough to go beyond f2. When returning from f16, the motor spins continuously until I shut my canon eos RP off. I suspect it's a problem with the electronics or the motor itself since this happens without any aperture blades. I don't know how to continue with fixing the problem. Obviously the most sure option is to send the lens to Sigma, but as usual, it will cost more than what I bought it for.
These videos show the problems:

https://drive.google.com/drive/folders/189HuRle9z-o9dCjoH2JDADqLvaZjNQ3X