Have an assembly with two configuration, with a couple of virtual parts (tubes) for either configuration. The tubes suppress or not based on the assembly configuration chosen. When I choose the left configuration, everything is copacetic except SolidWorks is reporting an error (red colored parts). When I check what is wrong, no errors... When I open the parts, no errors...
What do I do with the errors that are not an errors? <queue Final Jeopardy music>
What is "I've seen this before and it is certainly aggravating?"
You might try these things:
1. Ctrl Q to force a rebuild. Since there is nothing really wrong this should force SWX to realize it and be all happy again.
2. Suppress the unsuppress the component(s) or the mates associated with them. This is the same logic as above.
Is there some history to these parts, i.e., are you on SWX2017 and these parts were created in '16 or earlier? Sometimes it takes recreating the assembly of these parts to really fix this. Suppress the parts and then insert new copies of them and mate them accordingly and see if that solves the issue.
Let us know what finally does the trick.