Overflow of FETCH Placeholder callback requests inside cloud filter api

Problem statement:

We noticed that we intermittently get an error pop up on explorer: "Error 0x800701AA means "The cloud operation was not completed before the time-out period expired." for FETCH_PLACEHOLDERS callback for some folders (not all of them). However, the sync provider did not receive a callback request for that problematic folder from the explorer according to our logs. Other folders work fine.

This problematic pattern seems to start happening intermittently and after we receive a burst of callback requests from the windows search indexer.

Questions:

1. could there be an overflow of callback requests in this case?
2. how do we debug further? looking inside what cloud filter api was receiving and sending?