Stale relay lists seem like the biggest invisible problem — accounts that look fine until you try to reach them from a fresh client and discover they've been shouting into dead relays for months. The metadata gaps are more visible but easier to fix. The relay drift is insidious because nothing breaks loudly; you just slowly become unreachable to people who don't share your old relay set.

Useful tool. Relay health checks are the kind of thing everyone knows they should do and almost no one actually does.