When you selected 23 31 and 37 and DVB-T2 what signal strength and quality was shown ? If you didn't notice simply select manual tune DVB-T2 and manual tune and each in turn. If you get a strength and quality and then scan, how many channels does the box find on each of the above. I think you may fallen foul of a bug I found in manual tune.
I got all the channels after switching transmitters but they failed to save properly.
I seem to have discovered a very strange bug in smart retune.
Having a spare Vision log 36 I decided to see if I could get Com 7 and 8 from Sutton Coldfield. Having connected it I did a smart retune without issue, however signal strengths aren't as good as Lark Stoke and there's not a sniff of COM 7 and 8, so I reconnected the Lark Stoke aerial.
Smart retune found the usual 145 channels. After saving the box reports no or low signal on PSB 1 and 2. Quick check showed 87% signal 100% quality on both. Tried a manual scan which found the channels without issue.
After saving still no signal reported. A full auto retune worked fine but I did of course have to re-enter the schedule, losing the one I was watching to see if it auto-deleted.
One thing you can try is fit a variable TV attenuator and find the point you can reduce the signal level on the above mux frequencies and still get 100% quality. Now try a auto retune.