I saw an interview the WeBull CEO gave yesterday, and he offered a plausible non-criminal (at least on their part) reason for why the brokers were putting stops on buy orders for the meme stocks. The brokers were told to put the restrictions in place by the clearinghouses that do the actual processing of the transaction, because the clearinghouses didn't actually have enough cash to post the collateral required, because the company above them (it sounded like ETC, but I'm having a hard time finding an actual name) had set the collateral requirements for the meme stocks at 100%, when they're normally 2-5%. If this is true, then most of the brokers are helpless to do anything and weren't trying to screw over customers. If there were SHUT IT DOWN messages being sent, they might have gone to the people who set the collateral requirements rather than the brokers. What it wouldn't explain, though, is RH forcibly selling customers' shares on the dip.
As I understand it, the signal to start selling is after the people holding the shorts start placing buy orders in significant numbers, plus as long as you can wait to let the target price of the buy orders be forced up when they can't close at the lower.