I just flew with JAL and purchased inflight Wi-Fi, hoping to get some work done. A few minutes after I connected, not only was it slow (which I would understand), but various office applications wouldn't connect. When I tried to do it via websites, it asked for two-factor authentication, which required my phone to be connected.When my phone connected, my PC got disconnected. Once I got my PC back online, it asked for authentication again. As a result, I ended up just crafting emails offline with occasional browsing.This was simply the worst Wi-Fi experience I've had. I'm curious if this was a common theme, or was I wrong to assume I could work during the flight?
All Panasonic wifi systems are painfully slow, it's not unique to JL. As for your other issue though, there's a workaround. The wifi system is quite intentionally designed so you can only sign in from one device at a time, so that is what caused your problems, again not something unique to JL, all similar systems operate the same way. But the workaround is to sign in from either your phone or laptop and then tether the signal to the other. Not all phones can do that, but I know Pixel can. I think most laptops can do it, just requires multiple antennas. You could also do the tether on Bluetooth or USB if using older devices and neither has multiple antennas.
Another workaround is to ditch 2FA on trusted devices. Perhaps you're on a corporate governed MS account where that's not an option, but I've never had to do 2FA on my own PC since I signed into MS 365 on it the first time 2 years ago. I don't use the online version however, that may be different. I have the downloaded and installed apps.