OK, I've now tuned all 113 stations on Hannington (South) transmitter. It turned out that I had to change the direction of my aerial thro' 90 deg, altho' Hannington hasn't moved. Perhaps, as you suggest, a relay was taken out, altho' I thought I was pointing at the strongest signal.
I had to massage the tuning data of my TV tuner programs, cuz the muliplex channels and frequencies had changed over the switchover. Indeed a couple of the frequencies on the official Freeview site
for Hannington were slightly out (by 0.2 MHz) sufficient for one of the TV tuner programs to skip over them until I amended them based on data from the other TV tuner program.
As regards the OP, I have no experience of WMC but perhaps its tuning data has run into the same problem.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC