IBestBetRepository cache fails when there is a large number of best bets

I am working on a solution with a large number of Best Bets. Over 800 in fact. It appears that, somewhere along the line, we passed a threshold in which IBestBetRepository stops using caching. That is, either best bets fail to be inserted into cache, or they fail to be retrieved from cache. I don't know which.

We have code that queries best bets via IBestBetRepository.IList(). We noticed that calls to this method were taking up to 45 seconds to return. This happens every time. We query it once: 45 seconds. We query it immediately again: 45 seconds. Again: 45 seconds. And so on. Clearly, no caching is taking place. After deleting the best bets down to <200 (from >800), the response times significantly improved.

We mitigated this issue by adding our own IBestBetRepository intercept/decorator which manages the list of best bets in ISynchronizedObjectInstanceCache itself. So our solution is working great. But, to be a good citizen, I wanted to report this issue to Episerver for internal troubleshooting. Thanks!