A little background
I am a Cox Customer in Santa Barbara, CA. Cox has deployed Switched Digital Video (SDV) in my area, and as such it requires an Tuning Adapter to be attached to the TiVo to allow it to tune those specific channels that are SDV enabled. This, combined with a CableCard allows me to access all channels in Cox's channel lineup. Before the Roamio, I used to have the original two tuner TiVo Premiere. I never had a failed recording with SDV unless the box locked up, which happened maybe once a month, but other than that, I had no problems.
When I got the Roamio, it became pretty clear that having 6 full tuners along with SDV was causing an issue. I didn't realize it at first but after reading the reports on this forum, it became clear that I wasn't the only one. I didn't have an issue with the CableCard not being able to tune the 5th & 6th tuner, but a combination of that issue along with SDV was causing recordings to just fail midway through, or not record at all. Seeing V53 & V58 errors became commonplace.
In the main thread (Tuners 5 and 6 Not Authorized
), it was suggested to disable the 5th & 6th tuners as a way of temporarily reducing the frequency of the tuning issues. So I did that, and the issue became less frequent, but it was still happening.
Then came 20.3.8, included was a blurb from Margret about how it will now "retry tuning requests after a Tuning Adapter fails to respond". I was skeptical, but I figured it couldn't hurt. Boy was I wrong, all of my tuning issues were resolved! Three days later I re-enabled tunerr 5 & 6 and it's been going great ever since.
I have attached a spreadsheet detailing about 38 days of recordings. The recording bitrates in red indicate a failed recording, green indicates a successful recording. Because of the way the SDV failure exhibits itself in a recording (The TiVo records an empty signal, so the duration is as if it was successful, but the actual size on the disk is reduced and the resulting bitrate is low), I know that a fully successful recording averages between 11.30mbps and 11.70mbps. So anything less than that is a failed recording, I spot checked about 20 of those *bad* recordings and they all had tuning failures at some point in the recording.
As you can see, disabling tuners 5 & 6 help a little bit, but did not resolve the issue. However, 20.3.8 completely resolved the issue and I am now running with all 6 tuners.
Thanks to TiVo for solving this issue, and thank you to moyekj for the awesome kmttg software that gave me the information needed to verify this with hard data.