Now we have some possibilities don't we. Now that is being helpful when you list several possible reasons. I am 100% for self help but expect to gather knowledge from this site and I think so do others.
The most important message I have learned from my time here is that, water quality is gold!
When someone posts the water quality is in good order and you want to reply to help the poster... You have to assume they have checked the water quality and are competent to do so.
I don't think anyone here is looking for a 100% correct diagnosis when posting anything but more like scenarios of possible causes. Again, I have learned that water quality is the number 1 factor in many of those possible scenarios so that is why it comes up so often.
Perhaps I am unlike many aquarist and actually do check my water quality often.
I liked your post batman. 1077, I have come to learn that your world rotates on water quality! haha I am not being sarcastic, your drilling that home encouraged me to read more into it and learn.
The main point that I would have thought important is that silver dollar fish are by nature shy fish. In ANY tank I have come to learn they will swim away from a person when they walk over to it. Perhaps there are exceptions, as there always are, but in 90% of the cases they move away by nature.
Another important fact about this fish is that lighting or reflective lighting will bother them. If your substrate is brighter in color and your lighting is not subdued they will freak out.
The primary reason any fish schools is for protection. If a tank has no threat, the need to school decreases to almost none.
I'll continue to read, learn and challenge ideas where I have thoughts.