I am seeing the same issue, but it is inconsistent. I have two very similar cases in my app in which I have parent tables each with 3 child tables. Each of the children references two other tables for a field lookup (not a part of). One instance works consistently as expected - deleting the parent deletes all children. But in the other almost identical set of tables, deleting the parent always leaves the children behind. I have inspected the table contents very carefully via SQL query to make sure that the references between the values in the tables is correct and consistent. All table keys are good, unique, and properly referenced. I have also carefully reviewed the “Is a part of” setting to make absolutely sure the child table is properly marked as such and is only the child of one parent table.I am working online and forced a sync after performing the delete. For the life of me I can’t figure out why one works and one doesn’t!
I will be opening a support case with AppSheet but I wanted to crowd source this also because it is a major problem for me and it sounds like there might be a big fat bug here.