My issue was (or appeared to be) the sensor assembly.
I brought a COMPLETE replacement part for an iPhone 6G. Once replaced, Apple Boot Loop continued, DFU mode did not work, nor did a hard reset, just a continual boot loop.
I removed the stock sensor, camera, shield plate and home buttons from the complete part and replace them with the originals from the broken screen.
First boot worked - unsure if this could be a boot hardware initiation issue, maybe some of these component parts fail and cause the Apple loop.
Hope that helps,
Will
RocktScience.co.uk