I had issues with my HTC M8 on both my CX's, one with the TomTom system and one with MZD. Sometimes it worked, sometimes it didn't, there was no obvious pattern to it. It got a bit better when I went to a Samsung S8, but by that time, I'd given up with the connected services, got a full refund for the 3 years from Mazda and started using Waze on my phone instead as the main sat-nav. (I mostly keep the inbuilt one on in 2D mode to see where I am in context to the surrounding area.) For a free app, its brilliant! Far faster that the inbuilt one for routing, very up to date and it's collaborative - it's kept up to date by users.
Alan