This isn't exactly the same but... a few weeks ago, I was finishing a 2D drawing (let's call it "A") adding a few more dimensions. I switched to another drawing (different part) doing the same... tweaking dimension positions, adding a few, and cleaning up. When I switched back to drawing "A" to adjust a dimension position I had just added, it was untouchable. You could see the dimension, it would show up when printed, but I just couldn't grab it with the cursor (it would not highlight). I could grab/move others, just not that one. So I shut down Alibre, maybe saved a few open drawings I had touched, and restarted Alibre loading drawing "A". The same dimension was still stuck as if it was not there.
So over the next hour or so while working on other aspects of the project, I made changes to the project's global parameter file which drove a change in the associated "A" part file. When I reopened drawing "A" and reprojected the views, the stuck dimension was now unlocked and would highlight when the cursor passed over it. I could move the dimension around as normal. (btw, I tried reprojection very early on, before the global parameter change, and that did not unlock the dimension.) So my guess is something in the drawing file "A" became (logically) corrupted, but because the associated part "A" changed driven by the parameter change, the drawing file was also updated and fixed the corruption.
So, not sure if my experience is at all related to your problem but thought I would mention it anyway. They may be related somehow.
