I tried flashing my phone with Samsungs Firmware but that wouldn't fix the problem either.
My phone is being "repaired" at Dynafix. Hopefully I will get a replacement of some kind. As soon as my phone returns I will post the results heren.
@ ShadowLea, I indeed had a Samung Galaxy S3 with the insane memory. After replacement of the motherboard, the problem was fixed. Now it's my spare phone
The second time they did a board swap. After 46 hours I got a freeze + reboot, but after that one, I haven't got a freeze+reboot since 65 hours. So it seems like the first freeze was an accidental one. When my phone freezes again, I will update this thread.