Well, the answer is yes and no.
This summer, I was travelling in Canada and Japan. When I first posted this thread, I was in Canada. I was using public wifi networks to play Pokemon Go as I did not have a Canadian SIM card with data. As I was using public wifi, this could have been why I was erroring out (connection was not strong enough). In addition, I tried taking on raids alone, with no help. Maybe the game was forcing me to play with other people?
However, while in Japan I was using a 4G network to play. I only errored out twice (missed my Moltres because of this), however, while in Tokyo I managed to successfully play a Zaptos raid and a Lugia raid.
To be honest, I don't know if this was a problem with my network or the number of people participating in a raid. The issue seems to have been resolved, but we'll have to see until next time.
According to Niantic support, they tell you to check the following:
- Make sure your app is up to date
- Use automatic (network provided) time and date
- Stay within range of the gym
- Check your internet connection
Hope this helps.