After an update from Apex 18.2 to 19.2, some pages with Interactive Grids started producing this type of error when saving changes using a "Interactive Grid - Automatic Row Processing (DML)" process:
ERR-1002 Unable to find item ID for item "SOME_NAME" in application "12345"
It's a bit of a sneaky one, because on the page itself you get no indication that there is a problem; it just doesn't save the changes. The error is raised, which you can see in the debug log, but it is not raised to the page itself.
I'm not entirely sure the update was the cause, but since the page worked fine before I highly suspect it was.
After 2 hours of debugging I found the cause. It turns out that the Query Only setting for any Interactive Grid column that is to be changed, has to be set to Disabled. If not, you get the error above - in 19.2 anyway.
You can find the setting here: IG Column "SOME_NAME" => Source => Query Only. Change this from Enabled to Disabled.
A quick and dirty query to find columns like this: