My help pane is unresponsive. Help!

Dear Folks--
The help pane of my RStudio has become unresponsive. Neither repeated returns nor topic refresh have any effect. Quitting with or without save does not solve the problem, though sometimes it will restart with the last help topic I tried to enter in place. I did an upgrade to the latest RStudio. Still same problem.

Unfortunately, I do not know how to replicate this problem because I do not know how to make it stop, which would be the first step.

I have occasionally had problems in the past reminiscent of this, and they all turned out to be due to long calculations or, e.g. opening a huge object in the object inspector. But I do not believe that is true in this case.

I have some suspicion that the problem is related to one or more add-ins, but this makes sense only if they can affect RStudio without being explicitly invoked in the current session.