Line numbers disappear after scrolling down and then up on larger documents

[davidye]

On larger documents, scrolling down and then back up causes the line numbers to disappear.

Repo:

Go to https://codemirror.net/6/
Copy and paste empty new lines into the editor until it's > 200 lines (not sure what threshold is exactly)
Scroll back to the top

Screenshot:

Using Chrome 84 on OSX.

[mischnic]

Sounds similar to #240, maybe it's already fixed but the website wasn't updated