In the Phosh Beta9 thread I posted a remark regarding the fact that both mobile and wifi connections remained dead on my phone when it came out of (deep) suspend.
Since switching to the unstable branch and updating a couple of days ago I can happily say that this behavior no longer seems to be happening, at least for the mobile connection! It seems to come back up every time, and fast too! 
I’ve also tested calling the phone a couple of times when it was in deep sleep for about 30 minutes, and it rang every time. So fast even that I was wondering whether the phone went into suspend at all, but that seems to be the case since the battery is not being drained like crazy.
Really happy to see this massive fix, thanks for all the efforts! Will use the phone as a daily driver for the coming time to see how it holds up! 
Edit: of course, I knew I should not have posted this, now I jinxed it 
After having updated the phone and rebooting, the phone is now regularly losing connection to the modem when coming out of suspend again, which is only ‘fixed’ by a reboot. I’ll try to obtain some logs when this happens. I have the idea that it’s happening more often when wifi is also active - but that might just be my imagination as well.