>> The question is, why did this surface only with the latest Emacs
>> update?
>
> actually, it isn't necessarily the latest emacs update, though it
> probably is a one within the last several weeks. i started noticing
> the problem a week or so ago, but didn't have time to investigate
> until yesterday. i may not have done an update for a week or more
> until before i first started seeing the problem.
Could you try to track down why the error happens?
One way I suggest doing this is to go through the various `error'
calls inside run-with-timer, and make them additionally print a
message or save something to a variable. If we can find out which
`error' is being triggered, we can figure out whether it's a problem
with Emacs, or with your customizations.