I was curious to see if anyone else has experienced this issue in ArcGIS Pro. I imported a polygon feature class from a FGDB downloaded from AGOL, into a new FGDB with a feature dataset, and after creating topology rules of must not have gaps, it seems some of my polygons were grouped/merged together, but the same amount of records exist.
This what it looks like when I select this highlighted poly in the original layer.

This is what it looks liken when I select that same poly in the imported layer with topology.

If found this post that has a similar issue, but for ArcMap: https://community.esri.com/t5/arcmap-questions/polygons-merged-when-added-to-topology/td-p/1277299
Unfortunately, Repair Geometry didn't seem to work for me in this situation. But, I'll just work out of the original feature layer without topology.