Yeah, with the Motorola SB61XX modems, it's typical that they display about several hundred to a thousand Uncorrectable Codewords for each channel right after it boots up. After that, the Correctable and Uncorrectable errored codeword counts will normally slowly increment if you're getting good downstream signals.
On my SB6121 modem, the Total Unerrored Codewords counts are roughly the same, as well as for many of the SB61XX signal page screenshoots I've seen posted in this forum, though a few of them have shown one channel having a count of up to twice as much as the others.
As the errored codeword counts for your modem look good, and you say it's operating OK, I wouldn't worry about that anomaly.
FWIW, for about the past week, my SB6121 has been showing a preference for the highest frequency channel (not the "Favorite Frequency"). I suspect that it is just random chance based on how busy each channel is.