Xcode stuck waiting for device to unlock, waiting for symbols, etc.

I have chronic problems with the connection between Xcode and my phone.

I plug the phone in and Xcode says "Waiting for phone to unlock", but the phone is already unlocked. I try locking and unlocking it, but nothing happens.

If I can get past this problem by disconnection and reconnecting the phone a couple of times, it gets into the "downloading symbols" phase and never gets out of it.

Finally, even though I have checked the "Connect via network" option, it never works, and I can never connect unless I plug in the phone with a USB cord (yes, the phone and the computer are on the same Wifi network).

Some days this is just an annoyance, but some days (like today) I really need to test something on my phone for a customer who's waiting for it, and I cannot. The thing I'm trying to test involves sending text messages so I can't use the simulator or even an iPad. What can I do to debug this problem?