I still don’t understand why get a “Could not update row” error for a step that just waits and doesn’t update any row.
FWIW, my next suggestion is try troubleshooting based on @SkrOYC 's good point that timestamp keys can be fragile. Maybe try modifying the expression that populates your key column to UNIQUEID()–even just temporarily for one cycle in order to see whether that resolves the issue.