Mortage Credit Rating not the same as Bank Credit Reports

[Xela Batchelder]

Working on qualifying for a mortgage today.  My credit rating is super high according to my Chase ap (experian), and my discover card (trans union).  My score is super high (not sure it is safe to mention the score here), well into the 800s on both of these reports (about 6 points difference between the two agencies).  

When they pulled for a mortgage the Experian was more than 82 points lower, and Trans Union was 113 points lower.  He said mortgage loan reports are different, but admitted nothing weird stood out to him.  But my middle score ended up 10 points lower than I can for a loan with that bank (ok for other banks, but bad rates).  Just annoyed I walked in thinking I had amazing credit, and these mortgage scores are so far off from what i've been seeing from my banks for years now.  

Since I don't know what is wrong, I don't know how to get it up, or just really weirded out by being so blindsided today.  Any advice, or did anyone else know this was a thing?  How can I learn how to improve it?

Thanks!