Recently replaced screen/digitizer on Droid Razr Maxx HD. Screen now works fine.
Unfortunately, the phone appears to be suffering from a boot loop - it reaches animated graphic part of startup then freezes and reboots.
However, after an hour (sometimes less) it does finally boot up and phone appears to work fine!!

Performed many factory resets and wiped cache etc. No luck
Also done this after full battery discharge.
I gather a flashing of the ROM may help but it looks like my version of Android may not be supported?
Version 9.18.94

Any hints or info would be much appreciated