I faced the same problem as described here:
The Skeletal Mesh disappears each time I restart the UE, it appears back after recompiling, but the details tab is always empty.
The Capsule component, however, never disappears. Both of those are defined in C++.
However, the solution does not help. My UE version is 5.4.4.
How can I fix this?
What is the least bugged UE5 version?
Similar things happened to me like certain components not being visible on the viewport or some options in the details menu being inaccessible after I played with the project files. My case was the result of a corruption, but can it be also what’s going on here? Anyways, does this happen to a specific blueprint? (You said skeletal mesh at first but then mentioned capsule component so I assume the mesh of question is inside a character blueprint) Could you try creating a brand new one and see if you encounter the same issue on that one as well?
Wait did you say C++? That corruption thing I mentioned can also occur if the code doesn’t get compiled properly before the editor opens up. In fact, I just remembered that my similar issue was also due to that reason and not playing with some files myself. If your character blueprint have dependencies on a C++ class, it’s healthier to launch the project from Visual Studio. (Though it’s funny that I don’t encounter that issue on 5.4 contrary to you, while I used to on 5.3 
)