Currently we check whether we should stop fetching from our current sync source and re-evaluate our sync source selection every time we fetch a batch from our sync source. Part of the check for whether we should change sync sources includes whether we are currently caught up to our sync source (iff our sync source in turn has no sync source and isn't primary). If the batch we just fetched is the one that makes us caught up to our sync source, now we'll wait for another batch to time out its awaitData timeout before changing sync sources. If we checked whether we should re-evaluate our sync source at the end of applying a batch, we could change sync sources faster in the case that our sync source has become isolated from the primary