It's not possible to select an invisible tempo marking line without text (in order to delete it)
1. Select multiple bars
2. From the tempo palette, add a tempo marking with a line going over those bars (e.g. accelerando)
3. Set the marking as not visible and remove the entire default text in it
4. Unselect the marking
5. Attempt to select the marking line again in order to delete it
Expected result: I can select the line and press Delete to delete it
It is not possible to select the line at all. It's not possible with one click or double-click. I also tried with Alt+Right/LeftArrow used around the first note in the affected bars, that didn't work as well.
Select all the affected bars. Set the visibility of all selected elements to "visible". The line should become visible, and then it is finally possible to select and delete it.
Possibly related issues from v3:
I also attached a WIP score file where this problem happened to me. I hope that helps.
See #290044: Lines with "line visible" disabled can't be selected by clicking the invisible line