No Turn by Turn Notifications when hiking (walking activity)

I have used my 6x on about 4 or 5 hikes now. Last week I updated the firmware to 4.30 and the next day did a hike - and the Turn By Turn notifications worked perfectly. I was quite excited! Then did another one this weekend and as usual, no TBT.

In all cases, even the one where it worked, I created the route in Plotaroute, exported it as a FIT file, then copied it to the /newfiles folder on the watch. It was my understanding that the watch generates the TBT as it imports the route. There are no Waypoints.

These are all about 10km hikes around local trails, with a lot of turns.

I actually use a Walk type activity renamed to Hiking. In all other respects, the watch navigates around the route ok.