Updating to 2019 R2 caused all sorts of problems with my TopNav HTML5 projects.
Broke the ability to use the Search box (??) in topNav help output - Cosmetically it looked fine, but the search button didn't work at all.
Broke the display of the menu proxies that we were using for context-sensitive help navigation in the help topics - big empty blank space where the miniTOC should have been.
Broke the display/use of the TopNav menu in Chrome (reported that one as a bug before we noticed the above 2 bad behaviors).
My team's going to be reverting back to the older 2019 patch level Flare and/or 2018R2 because was at least non-intrusive.