mattwnz:
The only problem I had was a faulty infotainment system. It would freeze or lag, or fail to boot intermittently on startup. They ended up replacing a module in it which fixed it, but it was frustrating to get it resolved as they thought firmware updates would fix it, which didn't. But come across other owners who had have had similar issues with it.
The old MZD Connect system was terrible. It felt like a high school computer science project. The newer system I have in the CX-30 is much better but I tend to always use CarPlay anyway.
The other issue is the 6 month service cycle when it is 12 months overseas is another annoyance.
It was a six month interval on my Mazda3 but 12 months on my CX-5 and CX-30. I'm not sure if that's because of Mazda extending the intervals on newer examples or whether it's because of my Mazda3 being diesel, but definitely something for the OP to keep in mind when looking at second hand Mazdas.