Hi @rohnin, welcome to the Duo Community! Thanks for your question. Hopefully, someone who has used Duo Mobile in China before will comment, though I also wanted to weigh in with some info about this from the Duo side.
Did you have the user try any of the steps in our iOS Push Troubleshooting Guide? Duo Push should work on iOS without issue, as you’ve noted in your post above. If the user’s issues are not resolved after trying the steps in that guide, you may want to open a Duo Support case to investigate further.
FYI to help other readers who come across this post - I think the Duo article you read which you’re referring to is this one: Does Duo Mobile work in China? That’s a great place to start with this question, and thank you for letting us know you already read it!