Well, it's not just Tivos that have a problem. As I said, my DirecTV DVR also has the same problem. At least for my DVR it's not related to a channel "scan" since it can't do a scan, it's totally reliant on guide data. If a channel doesn't appear in the guide data, or is incorrect in some way, then the DVR can't record it, even though the signal is passing through the DVR and can be seen live with the tv tuner.
Based on my experience dealing with the same problem during the digital transition, I'll take a large bet that the problem is either with guide data from Tribune Media or with bad PSIP data being provided by KCEN.
You're lucky to be on a hill. KCEN is the toughest signal for me. I can see the lights of the KXXV tower at night at compass heading 192. KWKT is about the same distance at 195 degrees and KWTX is at 193 and roughly the same distance. So, all three of those are easy to grab even with rabbit ears. KCEN is further away and at 161 degrees, so it's a bit of a pain.
DirecTV since 1999
Sony 34" HD KD34XBR970
HR20-700 HD DVR