First time I’m seeing someone use Pace as target for a ride workout…
Pace is not a valid target for cycling workouts. This is nowhere specifically mentioned AFAIK, but you can’t setup pace zones for the Ride category on the Settings page.
The reason is that Pace (speed) for cycling is very unreliable. It is to dependent on terrain and wind.
Why don’t you just set something like 5h15m Z2 HR?