I've noticed a couple of dragon's I've killed since updating to 1.7 won't let me absorb their souls. Anyone else having this issue?

I've also noticed that many dragons I fight since the patch have low-res models and textures until they start burning up. Is there a fix for this?

Dragons that spawn at Dragon Lairs will never give souls after the first kill. This has been noted since release and is generally accepted as normal game mechanics. As for low res dragons, saving and reloading will usually fix this glitch.