Having read all the replies to this thread, my feeling is that as soon
as LUL start dealing with a "light stuck on red" then the more worried
I will be about safety.

The term "signal failure" is a bit of a misnomer - it indicates to the
general public that the signal mechanism isn't working, when, according
to TfL, it means that the signal has failed to go back to green.

The current system strikes me as fairly robust, and I think it would be
difficult to solve it all at once.