sudden shutdown when attached to keyboard

After some months of not using my Surface Book 2, I noticed that it won't charge when attached to the keyboard.

I detached it manually with 6th holes method and charged it separately.

Every time when I attach the tablet to the keyboard it suddenly shuts off, even in UEFI screen. There is no way to start it when attached, eventough I used forced shutdown with vol up+on buttons.

If I charge the tablet attached to keyboard the detach button flashes red all the time.

I cleaned connectors with rubbing alcohol many times.

I let both tablet and keyboard for around two weeks in order to drain the battery.

I have even done a full reset but the issue still on.