When I do turkey breasts of 6-7#, I always experience a period of time where the IT stalls, usually in the 155-160F range, so to me that part is normal from what you have said. I usually need 4 hours or so to finish at 6-7# turkey breast to an IT of 165, and typically I am setting the smoker to 225F.
The other part of your story is concerning...I can't explain why your smoker temp only got to 139F if you move the temp setting to 250F. This leads me to think that your heating unit may not be working, but I would suggest another smoke to confirm this. The other temps you mentioned for the turkey breast, assuming you were set at 225F, seem about right. I am not sure where you had the temp set for the ribs, but 205/210 would be low if you were set for 225F.
The other test I would suggest is to ensure that your ambient temp probe is calibrated...you could test this by checking the air temp in your house (should be close to the setting in your house) or try boiling some water for a test to make sure it reads close to 212F. The other thing I have noticed with my smoker temp probe is that it will sometimes read lower than the actual temp in the smoker because I have it sitting on the top rack of the smoker rather than on the rack with the meat. Just some additional thoughts...