1- you changed the place where you hosting these two M21s
2-you getting an error that says in plain English
250 Power input undervoltage protection 0. code: 0x00020000
I can not think of any issue aside from improper voltage input , if i recall correctly the psu has a label which states 200v-250v , which does not match the 240v mentioned on their website, I run mine on 220v and it works just fine, i am averaging 54.5-55th for an alleged 56th m21s, i guess I could get 56th on 240v, but the fact that miner runs just fine without any error on 220v then so should yours, but if it's anything below 220v then that might be an issue, also just because the other gears like T17s and M20s run fine, it does not mean there is something wrong with the ms21s, each PSU has it's own voltage specs, so make sure you measure the voltage you feeding those gears with.