I can repro, same version of Chrome, Windows 10.
For me it only happens to me when Chrome is in full screen mode
And also
- only happens in Chrome
- the issue disappears when dev tools are opened.
- it only happens when I scroll using my mouse, it does not happen when I scroll using cursor down key
- I can only reproduce on your forum, not in another forum with the same font
- it happens on your forum in safe mode as well
I would reckon it’s a browser bug.
EDIT
Found a similar bug report here https://bugs.chromium.org/p/chromium/issues/detail?id=1363981
Repro https://codepen.io/AleksandrHovhannisyan/pen/oNdZxjJ