TLDR; Replace the corrupt SprungWheel BP.
I had the same problem in 4.20.3. except when I changed back to UStaticMeshComponent, the details panel remained blank. even after restarting Unreal.
Then I realised I had to comment out the CreateDefaultSubobject lines, build, uncomment and rebuild, the details panel then appeared. and was able to keep them as UStaticMeshComponent. this tactic wouldn’t work for USphereComponent though. those panels would never appear.
Then I discovered I could make the details appear in some weird format by changing VisibleAnywhere to EditAnywhere. but I think some options were missing, like Simulate Physics, MassInKg etc. though it’s all jumbled around. maybe they are there somewhere.
After countless re-compiles & engine restarts, I managed to get the USphereComponents to show somehow. but then the AxleWheelConstraint details wouldn’t show… what a mess.
After more digging. I learned that the issue is the BP is corrupting/failing to adapt to changes in the source files. So I created a new BP of the SprungWheel class and all was visible as it should be. Kinda ***** that we have to recreate the BP every time we add/change components. but at least it works.
Side note: I recreated an animal friendly Infinite Energy Generator