The question here is, is this a transient message or does it always happen. If transient, ie happens 1 time out of 20, ignore it. If it happens all the time you need to address it.
Most frequently this is a problem with 1) indexes needing rebuilding on the merge system tables, 2) locking with other merge/user processes (you need to limit the number of concurrent merge agents running), 3) querytimeout set to too low a value.
Set QueryTimeout to a larger value and see if that helps.
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