If I hit delete the time signature stays (e.g. is being hidden), when I cut it, it disappears:
This behavior does not apply to any other time signature.
Maybe something was messed up in this project (no XML-import)?
Time signature problem.dorico.zip (1.11 MB)
Try deleting the barline instead of the time signature. (You’ve created a single barline here for whatever reason at some point in the project’s past.)