Geany invisible underscore

Same issue, Ubuntu 20.04

The problem is well described here:
https://github.com/geany/geany/issues/1387#issuecomment-287537022

Some fonts write underscores below descenders but don't include that in the declared font height, this is technically incorrect and confuses the layout software in Scintilla (the editing widget Geany uses) so insufficient height is allowed for underscores.

The solution is to either change font or to instruct Geany to make line height bigger:

Tools > Configuration Files > filetypes.common

[styling]
line_height=0;2;

It turned out that the problem was with the Monospace font. This happens also with other programs, such as LeafPad if they use that font.

The solution was to change the font to something else - "Lucida Console" in my case.

Edit: It seems that changing the zoom fixes it, too. Some zoom levels have invisible underscores, some don't.

For future reference, I had the same issue with Monospace 14 in Kubuntu 16.04, and it was solved by installing the recommended nvidia driver for my graphic card.

Edit: Despite the anonymous downvoter, this solution worked for me and I discovered it by chance. It means that it is a display problem. I didn't find any reference to this with search engines, so I'm pretty sure it can help someone to find it here.