Something does not quite make sense.
It is still not necessary to scan channels using all tuners, as long as the channel type is the same. If you used a DVB-T2 tuner to scan for channels, it should be sufficient.
Have you tried simultaneously running (recording or playing live) two HD channels? That might force MC to load both of your "7231 DVBT" tuners. Unless the second tuner (the one that has been giving you troubles) is reset somehow, you may still get the same error. You can do an experiment, by putting the "7231 DVBT Tuner (1)" device on top of the device list, and try playing an DVB-T channel.
Your new log still shows that peculiar "ATSC" pest. I think I have tracked it down to the fact that at one point in time, you might have tried playing an ATSC channel using it (not just setting the tuner type to ATSC, but also play an ATSC channel). That may have made MC to save an ATSC "previous channel" in the registry, and trying to reload the ATSC channel. This action forced the channel type to ATSC. When MC tried to set new channel, it skipped doing it because it detected inconsistency in the channel types. The following log entry shows that setting of channel is skipped:
CDVBChannel::Set:Network type: this - ATSC, other - DVB-T
I am changing the Set() code so we will no longer skip the channel-setting when there is an inconsistency in types.
Further experiment for you to do:
Check this registry key -
HKEY_CURRENT_USER\Software\JRiver\Media Center 18\TV Settings\
__?_pci#ven_1131&dev_7231&subsys_362014c7&rev_aa#4&28b85f88&0&00a9#{71985f48-1ca1-11d3-9cc8-00c04f7971e0}_{3ff44ee5-8547-402a-94f3-d40000020001}
and find the value of "PreviousDigitalChannel". If the value is a long string, like this "DTV 4220 (12360-4284)674000, 8, 9018, 202, 4, 0, 201, 200, 0, 0, eng, 201", showing a network type value of 4 (shown in bold above), then it is a DVB-T channel. If the string is significantly shorter, or the network type value is not 4 (3 for ATSC), then we have a wrong channel saved.