First smoke complete, with a hiccup

Hi all,
I completed my first ever smoke today. I smoked a rack of St. Louis style ribs, and an 8 pound bone-out pork butt.

I rubbed both meats the night before with a basic sweet rub. Both items went into my Smoke Vault 24 at 6:00 AM.

I used a modified 321 method on the ribs, going with a 311 schedule. The ribs were good. Next time I'll stick to the full 321.

The pork butt. Ugh. I ran the smoker temp at 225, or as close as I could keep it to that temp. After 20 hours, the pork butt was only showing an internal temp of 185. I finally gave up and pulled it out. It is very good, but not as tender as I'd hoped.

The meat had a heavy stall at 160. It seemed like it never fully recovered. Progress was extremely slow after 160. It would still make a gain of 2 or 3 degrees an hour. Should I have waited it out? What could cause it to only hit 185 after 20 hours?

I am using a maverick et-733 thermometer, hickory chips. I did fail to fill the water pan enough and it went dry once. Live and learn...

Any words of wisdom?

Thanks,
James