Tseal:
The bridge is on Hood lane which is just off Newlands Rd which is a short distance from Cloughton (which the A171 passes through) near Scarborough, in North Yorkshire.The road it wanted me to turn my imaginary artic around (as Hood lane is dead end) was someones drive way near the beginning of the lane.
I’ve had a look and yes, that height restriction doesn’t appear in TomTom’s mapping, and it would be better if it said “no route possible” or similar. But to be fair, the road in question only runs for less than 200 yards past the bridge in question before it peters out into a dirt track/fields.
So no, I don’t think you are doing anything wrong - it’s just that TomTom (understandably!) haven’t got that particular bridge on their radar…