ios 12.4.1 causing bootlooping on SE's?

I run an iphone repair company. In the last few days every single iPhone Se (total of 5) that has come in for repair (whether it be a screen replacement, battery replacement etc) have all bootlooped as soon as repaired. Itunes cant repair it (error 9) - on each phone I have tried new parts, new usb cable, different computer - nothing fixes it! every single SE i have attempted to repair has done this if it has ios 12.4.1 installed. Dr. Phone cant even recognise the device or system software - I have been repairing iPhones for a long time - but am at a total loss with this re-occuring fault. Has anyone else been having this issue?? If so, is there a fix - because so far I just cannot find it! Any help would be very much appreciated.

TIA

Mel