This problem started with version 20. Instead of going to the prior or next brush in the list, using comma and period sends the brush off somewhere else in the brushes showing. Downloaded the latest update and it worked correctly for one day. The next start up the problem was back.
I have a large brush set so I did some additional tests. There are areas in the set that the functions work properly but in other areas they skip around randomly. During the random selections, it often skips to other brushes of the same diameter, sometimes of the same shape, other times of different shapes but of the same size.