Ah, ok I see… yes, I have seen this issue before…
Try changing the RG container layout to column, then adding a row container inside it - I had this issue a while ago when the new responsive engine was still in Beta - it seemed certain RGs (especially those in Reusable Elements) didn’t like Row container layouts - but I almost always put a group inside the RG cell so it didn’t really matter, and I haven’t seen the issue in a while, so assumed it had been fixed in the main release…
But changing the RG layout to column should fix it (it did for me) - so give it a try…
I can’t answer why only some items are showing in the RG, other than to suggest checking your privacy rules and search constraints…