Wow. It really is a bug and I'm not going crazy.
I also lose station presets. I've re-entered the FM presets about five times. At seemingly random times* one, two or three just disappear.
For some time I thought I was doing something wrong, but I now have witnesses who will confirm: Six FM presets showing on six virtual buttons; scroll through them, all working, all there... couple days later, one gone, button blank, save it again.
* May not be random -- I'll be watching to see if it's anything I do. It could have something to do with using the right scroll wheel or clicking on it, but basically, I've sworn off that thing... too confusing anyway. One time it happened was after I'd done a firmware upgrade during the previous night, but when I called tech support about it I was told "NO WAY it was the new firmware, it must be you..."
I never use Sirius XM or the others except for USB. I think it's a bug Tesla should fix -- Elon's guys, apparently, do not agree.