That does not sound correct to me. What should fill up a cache over months? A cache is by definition a transient memory section, which is forgotten when the thing that holds it reboots…
Yes, Bluetooth receivers buffer to overcome temporary connection problems. It does not use any kind of permanent storage for that purpose I’m sure.
The only thing written to permanent storage is the pairing, but that doesn’t change after the fact. So no accumulation of problems there either.
Did you try resetting and re-pairing your AirPods when those problems occur? Was this always with the same iPhone?
So far I’ve owned two pairs of the second gen AirPods, the AirPods Pro and the AirPods Max. Not one of them is showing any connection problems, so I don’t think this is a bug with either the hardware or the software, but just a problem with some specific AirPods (I.e. defective units).