REASON 1

The purpose of this assertion is to make sure the configurable interval to re-trigger the auto-merge is respected. The original idea was to keep it at 5 seconds to pad some slack, however on slow test variants this seems not to be enough because a CSRS secondary could be very lagged causing this query to find no documents.

REASON 2

When splitting/merging chunks continuously within this loop, it can happen that the refresh triggered on the router when serving the split request goes to a secondary, not acknowledging the merge that happened right before.