I pasted a set of HTML tables from a web page, into a new document. That worked fine.
The problem happens when I start editing the tables.
Here’s a screenshot: drive.google.com/open?id=1dxQTv … FkeigSHo7G
Notice near the bottom, the vertical lines separating the tables are not connected with each other.
If I page down and then back up, the broken lines are reformed, which suggests this is a rendering issue.