Lines showing between abutting walls in Hidden Line

[Christiaan 935]

I thought we'd put this one behind us, and I'm not sure when it started happening again, but I'm getting lines appearing between abutting walls in Hidden Line where they shouldn't be showing (horizontally and vertically); my walls are perfectly aligned as far as I can tell.

 

Is anybody else experiencing this? 

Edited January 24 by Christiaan

[Christiaan 935]

I think this was something to do with how or, more importantly, when the Viewports were created because as I progressed with working on these Viewports I noticed that some of them didn't exhibit the problem. And when I created fresh new Viewports they didn't exhibit the problem either.

 

The file started in v2019, was converted to v2020 and then to v2021.

Edited January 25 by Christiaan