There are a few threads here regarding getting into the SatNav diagnostics section. Once there you can watch the system rotate round the radio stations frequencies trying to pick up a valid TMC 'provider'.
It's either not finding a 'provider' or it is but that station is not transmitting.
Surprising as quite a few FM stations are enrolled into the scheme.
TBH I only use the built in traffic as a backup now. I'm running a Garmin 2597LMT linked to their SmartLink service that comes in via my mobile. That traffic updates every 2 minutes compared to the built in 15 minutes and covers considerably more roads.
AFAIK Inrix provide the Garmin traffic and you can get a free mobile app to see how good it is.