Metastore's update service wrongly strips partition column stats from the cache in an attempt to update them. The issue may go unnoticed since missing stats do not lead to query failures.
However, they can alter significantly the query plan affecting performance. Moreover, they lead to flakiness since some times the stats are present and sometimes are not leading to a query that has a different plan overtime.
Normally missing elements from the cache shouldn't be a correctness problem since we can always fallback to the raw stats. Unfortunately, there are many interconnections with other parts of the code (e.g., code to obtain aggregate statistics) where this contract breaks.