Some sticks to FEP, Some don't...

Hi,I am using a Phrozen Sonic Mini 4k resin printer with their Rapid-Black resin. Usually works ok.Recently I printed two small items - one worked, the other stuck to the FEP film rather than the base-plate. I didn't know why this particular item had a failure, and included it in the next print with a different item.The same thing happened - the original item failed again with a 'stuck to FEP', while the different other item worked fine. So I have a 'stuck to FEP' problem - but only with one particular item. And at the raft stage - there is nothing on the FEP but a rectangular blob. Most advice about this problem involves roughening the build plate or increasing initial raft exposure time. But that would affect ALL items, and I don't want to change settings that I have found work well. There must be something unusual about this item which is causing the failure.Can anyone suggest what it might be? Or propose something I could change for just THIS item, rather than machine settings, which might make a difference?Thanks...