I usually load my smoker up and do 20-30 racks of ribs at a time for vending, and at 250° my St. Louis ribs are perfectly tender within 5 hours, no wrap, no spritz. Rain won't effect your cook time much at all as long as your cook temp stays the same. Higher humidity can actually help to steam the ribs and cook them faster. You alluded to a heat deflector and that could be the culprit...there's just no way that those ribs were getting 250° for 9 hours and not being totally mush or burned to a crisp. I've cook on kamados, offsets, kettles, cinder block pits, and now I'm cooking on a cabinet and I've never come across 9 hour ribs at 250.
Can you take a pic of your setup with the heat deflector installed, and where you had your grate probe? Note : those grate probes are usually very sensitive, so if you've got the probe near a hotspot it will pick up on that very easily. This could have led you to believe that you were cooking at 250 when you were likely cooking at 190-200.
Pretty much all of us are saying the same thing here...odds are that your probe is off in some manner...either bad placement or your heat deflector is doing something odd in that cooker that you weren't anticipating.
If you post some pics of your setup it might help determine what's going on at the grate level. How'd your chicken cook go?