Are you sure your smoker is running at 225? It seems to me that your smoker might be running a little lower than 225 if you can smoke for 6 hours and the ribs are still not done.
For doneness, I usually use a toothpick and if it goes into the meat with very little resistance, then it's done for me.
BTW, the ribs look so good right now. I wish I could get meaty ribs like that around here.
Mak 1, GMG Jim Bowie, Weber WSM, Camp Chef Flat Top, Weber Summit