As I have all my SoundTouch devices (SoundTouch 130, SA-5 and a SoundTouch Wireless adapter) in my cottage, I'm not able to test with the SoundTouch app since it doesn't present the services until it has contact with at least one compatible speaker.
BUT, after the fix to the bug I reported back in May got fixed (and it seems it's fixed in your version on the iPad as well) I've not had any problems.
As a wireless networking professional I can imagine that many of the problems reported in this thread are down to the network. There's often a lot of focus on the two peers in the playing: the app on the phone/table and the speaker. But the fact of the matter is that the networking infrastructure has a significant role in this as well. And though you would think that a wifi network is a wifi network, they can differ quite a bit as well.
It's not too uncommon by wifi vendors (whether it's access points (bridging devices) or routers/gateways (combined routing/NAT:ing and bridging)) to try to optimize traffic by filtering out traffic that is considered potential network hogs, and this often includes multicast traffic and/or broadcast traffic.
Since I can't look at how the SoundTouch device does discovery for the other services (the Spotify discovery is Spotify specific) I can't give the answer right now. But it could be that it uses broadcast traffic either to the global broadcast or local broadcast address (255.255.255.255 or 192.168.1.255 (if your network is 192.168.1.0/24)), and that the router/AP filters traffic for multicast but not for broadcast. What I do notice is that when using the Deezer app itself, it uses regular AirPlay discovery with mDNS. But Bose's app could use something else. (And theoretically there could be other things that affect the method chosen.)
Ideally one would do wireless packet captures to record the traffic and see what's actually sent and received. But this of course requires more skills than operating the Spotify app.
But until I get around to doing a more comprehensive guide on how to record wireless traffic (not promising one, but I'm tempted to do one based on all the problems people have, and the fact that wireless packet captures are really the best way to troubleshoot things like this) I would look in the wireless router or access point admin interface and look for any kind of broadcast or multicast suppression. You can also check if different radio interfaces(2.4GHz (802.11b/g/n/(and maybe even 802.11ax, since that supports 2.4GHz as well) and 5GHz (802.11a/n/ac/ax) are not segregated/isolated. If you have the same SSID (network name) on both radios there's no real way of controlling which channel your phone and speaker connect to. Of course, the segregation scenario is not likely to apply if other music services do work from the app. (But could be applicable for those struggling to get connection at all.)