I created an issue for this in github.com/textmate/bugs (https://github.com/textmate/bugs/issues/33), but perhaps that issue tracker isn’t monitored any longer.
After upgrading to MacOS 10.15 (Catalina), scrolling through a large file (>6000 lines) often does not properly paint the text. This can be temporarily corrected by dragging a selection over the missing text.
• OS version: MacOS 10.15 (Catalina)
• Textmate version: 2019-09-15 (v2.0)
• File language: HTML
Most recently, I noticed this when moving to line 3500 in the referenced file and scrolling downwards.