Painter 2019: Issue with long delay after first brush stroke

I have an issue with Painter 2019 where, after selecting a new brush in the brush selector, there is a long pause after the first brush stroke before I can apply a second stroke.

If I bypass the brush selector by switching to the simple layout, I can change brushes without this issue.  If I then open the brush selector panel, the delay re-appears (even if I don not use the brush selector panel beyond opening it).  Re-loading the simple layout is then required to go back to the state where the delay does not occur.

I have an open support ticket for this issue, but so far, no solution has been found.

I have tried the Painter 2020 demo, and it also has the same issue (though the delays are shorter).

Has anyone else come across this probem?