Heuristics for "typeclass instance problem"?

Stream: mathlib4

[Arien Malec]

Are there a set of heuristics for "typeclass instance problem is stuck, it is often due to metavariables"? I keep coming across this in Lean 3 to Lean 4 transitions and I don't have a metamodel for what the issue is, or what to try to resolve it...

[Gabriel Ebner]

The error means generally that TC search has failed, for whatever reason. I think right now the most common reason is bad instances, check #lint first!