I also have this issue. Seems to be completely random. I always run Internet Speed Test whenver it doesn’t work and slow internet has never been a possibility (speeds 150+ Mbps). Not really sure why some days it works, and some days it doesn’t but I just tried to load up three different flights at different airports (stock KPHL, stock KJFK and Pyreegue EGPH) and they all hung after Start Flight.
I’m getting very close to putting this product on the shelf for a month or so. The combination of issues is causing more frustrations than enjoyment.