I too have this issue with TM; but it seems it may be really something macOS 10.15 related ... i just had the same issue with a larger diff in Sourcetree.

Am Fr., 3. Jan. 2020 um 22:36 Uhr schrieb mocenigo <roberto.avanzi@gmail.com>:
The issue is still there. Also with the "defaults write
com.macromates.TextMate enableResponsiveScroll -bool YES" command and under
10.15.2 :-(

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Harald Lapp