when do you think caching starts to cause its own problems, you know, like becoming the slowdown itself?

we've been scaling our app and really leaned on caching, mostly Redis, for a good while. it's been awesome for read speed. but we're starting to notice higher latency spikes that seem to line up with a lot of cache churn and the work our invalidation logic has to do. it makes me think, when does the cache itself turn into a scaling problem, and how do we fix that? are there particular numbers we should keep an eye on