Do you mean for the same query, even if the memory configured for LRU is big enough, some of the cached entries for index still get purged?
If it is so, then there maybe some problems with the LRU cache I think. However, since your query is purely count-star without any conditions, I suppose the query may not use the index are all, which means the LRU cache may donot work for your query. From Smartisan T1
