Cannot delete old channel scan data

[Mike88]

Channel 2.1 (CBS) in Chicago was on RF12. Last week they transitioned to ATSC 3.0.
The "old" ATSC 1.0 went to RF19, and the virtual 2.1 was mapped to RF 19.

Now my HTPC with AverMedia OTA tuners is not able to receive 2.1. Doing a Signal Strength check in WMC indicates no signal on 2.x. FWIW it lists 149 channels. I did a channel rescan but that did not help.

If I go to the channel guide & click on 2.1, sometimes I will get a picture. But when I try to record, the picture disappears & I get a no signal message.

I did another channel rescan & deleted the old data first & proceeded with a new scan. Sixty channels showed up. But when checking Signal Strength, 149 channels show up.

I deleted the old data but did not proceed with another rescan and no channels show up. But when checking Signal Strength, 140 channels show up. Why did 9 get deleted and not all of them?

How do I delete all 140 channels from WMC? Maybe some old channel mapping data is corrupting things & clearing out all the channel data will fix the problem. Is there a data file in WMC that can safely be deleted, and which will be re-created with a new channel scan?

Thanks