This has been happening to me for a while. It first started when I downloaded the rain rig file. Everything was fine for a bit but soon I realized she was missing some textures. I did the whole find missing files, but she was still missing some textures. So when I did this once more her FK controls disappeared, and not only that but I had to deleted and redownload her so many times because the entire rig and mesh would disappear out of nowhere. And now this is happening again with a ball rig that I downloaded from the blender cloud site. I don’t know why this is happening but I believe this is only affecting the rigs I download from blender as I made my own rig and that has not been deleted or has disappeared. Sorry that this is so long but I hope there is a way to fix this. Thank you everyone for your time, and please do tell what may be happening here. Thank you.
Difficult to help, we need to see your workflow, to help better.