Losing punctuation in a topic

In one topic source file, all periods disappeared, except for those at the end of a paragraph. This includes periods in tables. It is also missing some semicolons and end parens.

The html also shows that the periods are missing. (I had thought there was some weird mishandling of the html.)

I could not find a reason why this happened, so I put them all back in manually.

I shut down RH and my PC for the day.

I turn on my PC and start RH. I go to the topic again and it is missing some of the periods I re-added.

Yes, this sounds crazy. And, yes, the punctuation was definitely there before.

Does anyone have thoughts about the possible cause?

I am using TCS 2.