In diagnostic mode as part of rollback to stable operation, while processing any tree for rollback to stable, if any clean page that doesn't have any updates more than stable timestamp, the page gets loaded into memory and verified whether all the updates on the page are less than stable timestamp or not? But once the verification is done, these are not evicted until the rollback to stable finishes on that table. During this time the cache usage gets increased more than the required. 

Immediately evict the pages that are read by rollback to stable operation to reduce the cache pressure.