As I feared. Thanks for that very pertinent input.
The few examples I read from Mamibear's link sounds like from people who can't even explain clearly how they got the GCs to load into Amazon, from a friend, new account, etc.
I've had an Amazon account for almost 12 years, have an Amazon Chase card linked as well as other Freedom and Discover cards as well as Amex MR cards.
I've had as high as $2500 this year, which is now down to about $900.
I've had the same address on file with them, made returns, not excessively.
Sketchy behavior will lead to adverse actions, not the balance by itself. Same as the UR or MR balance you asked about. IMO.