I have a 64gb Sandisk class 10 with no heat issues.
Have you ever tried resetting the phone?
64gb, Samsung EVO, Class 10, works perfectly, no overheating issues
Odd that support didn't ask you to perform a reset. On androids that works magic for many issues.
In the future no matter what phone you use if you have what looks like an unsolvable problem it is prudent to reset. This goes for any phone including iPhones. By the way my 128gb card came in. Strangely it was having problems getting files downloaded until I noticed my computer was low on memory. An important point here is those files that did download were corrupt and caused issues till I freed memory on my computer.
I've continued to experiment with the 128GB SD and found that when installed into my laptop, transferring files from the 64GB card installed in the G3, there is a message that the G3 CPU is overheating. Now these files being transferred are smaller than the 4 and 5GB VLC movie files. I figure the only way to get these files onto the 128 GB card is not to transfer them with the card in the phone but by another way, as the CPU apparently can't handle the large VLC files. So perhaps the fault lies not in the card but in the CPU of the phone. We'll see. More later.