Speed limit imposed on meetup

I did a meetup last weekend with a few other riders and all was fine for the first 124km. But then, our speed was reduced to about 17-20 kph. We tried stopping and restarting, all at the same time. We tried all hitting the same wattage, a level that would have us at 30-35 kph. We tried again and again but we couldn’t get our speed to go beyond that limit of around 17-20 kph. We even switched bikes. Finally, I ended the meetup and that resolved it, but we were not connected anymore (one of us could get dropped or separated).

This was for three riders in Singapore. One on iOS and two on PCs.

Any idea what this could be?