I recently noticed two issues with the HTC 10 while traveling.
First issue was with the WiFi calling, the phone would often fail to connect to WiFi calling with error saying it cannot connect to the service. At the same spot with the same wireless network (using wireless AC on 5Ghz), HTC One M8 had no issue at all connecting. I had the M8 in the past and remember I had no issues using WiFi calling at all. It would work only if I'm sitting very close to the router, and even then sometime it would not connect for a few minutes and give me an error.
The second issue was on the plane, I put the phone on Airplane Mode and wanted to turn on the WiFi to use the wireless connection on the plane. However once on Airplane Mode the phone will not allow me to turn on WiFi without disabling Airplane Mode first. I can't imagine that this is by design, I've done this in the past with other phones while traveling and just wanted to use WiFi when the phone is on Airplane Mode.