After each diff import the table `osm_poi_point` is fully rewritten due to a full update of the field tags. It is now good to do an a update, event if the content does not change, postgres delete and reinsert internally the record. Resulting in more write and internal table size raising. Note: not directly linked, but there is a problem in this case, the autocaccum is not sufficient to keep this table size moderate, but grow indefinitely.
poi
Docs
Read the layer documentation at http://openmaptiles.org/schema#poi

