I find the “Element will be detached from its associated plane” warning the perhaps second most annoying warning (the beam slightly off axis is the most annoying).
Sometimes there isn’t a good (read quick) way to fix this warning so we just leave it. Recently I have been working on a project where roof elevations have been changing quite a bit and occasionally the beams in my beam systems will detach themselves from their workplane…they are still in the correct location, but that warning now exists in my project. I have been fixing this by editing the beam system and clicking “reset system”, which doesn’t change anything I can see, but it quickly reattaches the beams in the system to the workplane that was originally set when the beam system was created.
I thought I would share this in case others could use it.