Q: WiFi problems with iPhone 5s and IOS 10

I have exact the same problem too.

I am supporting more than 1000 iOS devices in my company and all 5S  devices (about 600) are not able to connect to my hidden WiFi network. Users having huge romaning costs now when they are in our company locations in foreign countries.

I am working with an MDM software and tried many troubleshooting things.

How do we know if Apple recognizes this and works on a fix.
I can provide many logs and experience to maybe help here ...

I spoke with an Apple Support Representative on 10/10/2016 and was told that only 40 users (41 including myself) have complained about the iPhone 5s not re-connecting to hidden networks when using iOS 10 or later.  They continued to tell me that it doesn't become a "big" problem until 200 complaints, a "great" problem until 500 complaints, and an "outstanding" problem until 1,000 complaints.  Based off of what they told me it doesn't sound like Apple will be rolling out an update to fix it anytime soon.

I spoke for days with Apple, they would not admit it was a software problem, kept trying to blame my networks.  If you Google the problem you will find so many people are having the same problem.  It is most definitely an Apple problem.  Since I had talked to them last they must have fixed some of it, as all of a sudden the problem vanished, without me doing a single thing. I was at my AT&T store recently and they confirmed the problem is huge.  Unfortunately I think all you can do is wait for Apple to fix the bug, and in the meantime try to get reimbursed for your extra costs.  I would hope your cellular provider will work with you on it?  Good luck! :-)