iPad mini digitizer not working after screen replacement

Where are you getting your mini digitizers? If they were from the same supplier/batch, then it is possible you got some bad ones. On the backside of the panel, are there gold coloured or silver coloured traces bordering the digitizer? The fact that the original one works would indicate that the problem is not on the logic board.

The mini also has some gotcha's and is one of the more difficult iPads to work on. You normally have to tape down the bottom border and Home button flex to avoid ghost touching issues. Jessa put out a great guide a few years back, I would encourage you to go through it if you haven't already.