I (and others, I'm sure), appreciate everyone who is trying to help. That said, several of you are headed down the wrong path because you're making the assumption that this is user error. It's not. I, and others in this industry, have the same problem. To add a bit more detail to this thread, I'll explain.
In the audio and theater industries, we use a large variety of audio devices for our production. Most of these generate their own wifi network. Good examples this are X-Air series of wifi mixers from Behringer, or Mackie mixers, PreSonus, Allen and Heath, and more. Specific devices generate their own wifi network, which is then used by a mobile app connected to that network. The actual wifi network is not connected to the internet; it's just a local network for use by these apps. For example, I use several mobile apps to access one of my mixers. On Android (all versions) there are no problems, because I can connect to a wifi networks and Android doesn't care whether or not there is actual internet access from that network. However, since iOS 10+, Apple iOS DOES seem to care. It now just spins away trying to connect to the network , expecting to see internet access. Since there never is internet, Apple never allows it to connect.
One of the other posters offered a workaround (which is valid, by the way) of creating a "fake" wifi network with the same name, but which does have internet access. Then, connecting to it from an iDevice will succeed, and later attempts to connect will be fine (the network will be "remembered"). This is rather obtuse for a lot of folks, though. Imagine having to carry around a small wifi router with me to each gig, just to have to "fake" the client's network, get my mobile apps connected, then switch it all back. It's not only time-consuming, but really annoying. 🙂
What I'd like to see is an option in iOS (not in any version yet, as of 11.0.3) that would allow me to force a wifi connection to a network, even if it doesn't have a real internet connection. If this was available, then I'd have no problems connecting every time.
Roland (maker of some very high-end, expensive mixers) gets around this because their wifi network is identified as a "device" rather than an actual network. Connecting to their mixer is only a matter of answering "ok" to the question about connecting to that device, even without an internet, and then I'm good. I'd be happy to tell Behringer, A&H, PreSonus, Mackie, etc., to do the same thing, but they literally might not have the required hardware or firmware in their devices to do this. There are tens of thousands of these devices in use all over the world.
If anyone has any ideas on how to solve this problem (static addresses don't matter/work), or if Apple would be interested in adding the capability I'd mention above, then I'd be really, really, appreciative. 🙂
The best workaround I've come up with so far is to use a small travel router by TP-Link. I create a new network with the name of the mixer I want to connect with, give it no password, and then have my iPhone/iPad connect to that network. Once connected, I shut off the travel router, connect to the real wifi device, and I'm good. I just wish I didn't have to do this to get around this new "feature" in iOS 10+.
Thanks,
Bruce