On 8 Dec 2019, at 20:54, mocenigo wrote:

I HAVE GOOD NEWS (perhaps). I observed a similar bug in Outlook for mac. If
this is caused by the same bug in Catalina, Apple will fix it, and then it
will be useful for us as well. I know the argument is thin, but there is
always hope ;-)

A user on the cocoa-dev list is also experiencing issues with lack of redraw after scroll on macOS 10.15, they shared this screen capture from a user: http://eyalredler.com/stuff/catalina_glitch.png

Here the bottom part is missing, so it does very much appear to be a macOS 10.15 issue, also because in TextMate, line numbers and main text view are different views, yet both are “clipped” (missing updates) the same way, and the screen capture shared earlier, shows that what got redrawn is exactly 640 pixels wide, which is not an unreasonable tile/texture size when doing window compositing.

However, there is one “non-standard” thing that TextMate does: It opts out of responsive scrolling (this is necessary to properly synchronise line numbers with the document content).

Therefore I would suggest people affected to try to enable responsive scrolling, just to rule this out, run the following in a terminal:

defaults write com.macromates.TextMate enableResponsiveScroll -bool YES

You will have to relaunch TextMate afterwards.

The only side-effect of this is that sometimes when scrolling a document, the line numbers will scroll with a sort of elastic delay.