On 11 Oct 2019, at 17:35, mocenigo wrote:

I am not sure that it has anything to do with large files.

From the reports, it sounds more like a macOS 10.15 issue.

Is anyone not on macOS 10.15 seeing this?

The gutter and main text are actually two different scroll views with different code, the former being much simpler, so seeing gutter is also affected by this issue, it very much sounds like a bug that only Apple can fix.