There's not a lot of adhesive on the bottom side of the digitizer and a lot of stuff underneath it. You have to make sure the flexes are properly sitting within the device as even the tiniest amount of pressure will eventually cause the adhesive to let go of the digitizer.
The actual adhesive matters also. Was the adhesive initialled or did you apply some yourself? I find that the pre-installed adhesive is generally low quality and doesn't stick as well as a high quality adhesive, such as the Tesa tape you can find here on iFixit or pre-cut 3M tape from [https://bowlertech-adhesives.com/product/ipad-mini-premium-kit/|Bowler-Tech], which is what I use ( I remove the pre-installed tape first).