When I add dimensions, they are horizontally flipped at the beginning. How can I resolve this?

Example:
1.) I draw a rectangle.
2.) I go to Extensions/Visualize path/Dimensions to add the arrows.
3.) I click on 1 arrow. I go to Extensions/Visualize path/Measure path to add the units.

What I've tried to resolve the issue:
- I checked the manual and the forum for hints about dimensions, I watched a tutorial on YouTube about it.
- Idea: Maybe there is something wrong with the whole document settings? I checked the document settings but cannot see anything striking.

Inkscape version: 1.0.1
Operating system: Mac OS Catalina 10.15.7

Files imported from other programs can be tricky.

It can be helpful to mention the file is imported when asking for help.

I'd try this:

• Use File>Clean document to remove unused hidden defs.
• Use Object>Objects dialog to Select the  layer "Test Stand"  and change the layer to a group, by clicking on the icon in the T column.
• Click the ungroup button until all groups are removed.
• Clean the document again.

@Tyler: Thank you, I didn't have an idea that it was due to the fact that the original document was created with another programme.
I followed your steps, but did not manage to solve it. What I did:

• File>Clean document
• Object>Objects: click on "T"-column in the "Objects" dialogue.
• Object>Objects: click on "T"-column again to ungroup (?)
• File>Clean document

I've also tried

• File>Clean document
• Object>Objects: click on "T"-column in the "Objects" dialogue.
• Select all (Strg + A)
• Object>Ungroup
• File>Clean document

But nonetheless, I will create a new document and than it works. I whink I know now where the error lies. Thank you very much 🙏

Julia