Found what was most likely the problem, A turn restriction at the southern interchange for Beaver. And it's a mea culpa. I remember working on that interchange back in Oct when I found the SB on ramp wasn't even connected. Evidently in connecting it I somehow did a Q but not the following W on the junction.
Only question is why wouldn't those long distance routes go from Beaver to Minersville, down the minersville hwy to Cedar and get back on 15. It would add about an hour to the drive, versus 10 hours to go west via 80 then down.
But I also came across some areas where level 1's had been playing with the lanes so I've locked almost everything south of Fillmore, I'll get the stuff to the north later on. But locking it should reduce these occasional issues, this is the first I caused but the third or fourth time We've seen this problem crop up since I've been editing. So I'm confirming the green arrow at the end of each segment, then locking it.