Swapped the phone for a Samsung S8 and all same "3rd party" apps installed and no issues at all. Runs as expected.
When I took the XZ back they tested it after factory default and it still got warm.
Anyway our experience might be different for others but reading this forum our problems reflect what others had.
I did ask for help from Sony but to merely suggest try this try that doesnt cut it. This phone is a premium product. I was getting system UI errors. To me thats a good reason to take the product straight back.