__I've found a bug and checked that ...__
We use the mike version dropdown from mkdocs material insiders and we have two problems:
1.12.0-DEV and that version has a linebreak in the dropdown.This screen shot shows it: https://cdn.discordapp.com/attachments/520942709205237760/790887319636410389/unknown.png
For Problem
See Description
Live Demo: https://betonquest.github.io/BetonQuest/1.12.0-DEV/
1.12.0-DEV3.61.1.26.1.7+insiders.1.13.1
https://github.com/BetonQuest/BetonQuest/blob/master/mkdocs.yml
Could you please post the content of the versions.json which mike generates? With this information, it should be straight-forward to fix.
[{"version": "1.12.0-DEV", "title": "1.12.0-DEV", "aliases": ["DEV"]}, {"version": "1.11", "title": "1.11", "aliases": ["RELEASE"]}]
This is the original file: https://github.com/BetonQuest/BetonQuest/blob/gh-pages/versions.json
Fixed in the latest commit at Insiders:

A release is about to follow.
6.2.2-insiders-1.13.2 is out, which includes the fix.
Thank you very mutch