XPS 15 9550 - BIOS 1.2.29 - unusable USB keyboard and mouse
Updated to 1.2.29. Immediately experienced two serious problems with USB keyboard and mouse plugged into TB16 dock:
Keyboard does not deliver all events. For example, "key up" event is not sent, causing a key I pressed and release to repeat. This is true with normal chars, the spacebar, and delete (deleting all text I typed). Pressing keys here and there eventually gets out of this condition, but then it happens again, repeatedly. Makes typing on external keyboard useless.
Mouse frequently freezes up. Sometimes comes back on its own; other times, I have to unplug and replug to get it to restart. NOTE: if I plug into USB on 9550 instead, it seems to work reliably. That might also be true for the keyboard, but did not try.
Attempted to revert to 1.2.25 (the version I had before). Doing so deleted my UEFI boot, and I could not get past diagnostics or boot options. I found a procedure on how to manually create a new UEFI boot (named My Boot) and was able to start Windows 10 again.
It is normal after updating BIOS to have to re-enter the long BitLocker password, since I have that enabled. But after restoring to 1.2.25, it is necessary to re-enter every time I power up. This is a huge annoyance.