It’s a little disconcerting because you’re literally one „computer says no“ incident away from not being able to return to your own bed.
Literally zero paperwork was issued to fall back on so you’re entirely dependent on a DB server somewhere
Probably going to get a UK passport too just to manage risk. (Already qualify)
Travel to the UK is going to be really chaotic from 1st Jan when all BRPs expire, and 8th Jan when US citizens and other non-EU nationals require ETAs.
From HO website: "You may be able to use your expired BRP to travel to the UK until 31 March 2025 if both: your BRP expires on or after 31 December 2024. you still have permission to stay in the UK."
You might be able to bully them into accepting them because it’s in Timatic but there will be British residents who are blocked at least temporarily because of this.
Russian visas are machine-readable since 1997 to ease the DB request.