This is often a graphics card seating problem, but with onboard graphics I would suggest it may be either memory corruption (RAM needs reseating?) or - worst case - a motherboard fault. It may also be that the streaming was just too much for the RAM to take and virtual memory couldn't cope. Given that it also occurred when downloading mail I should start with reseating RAM modules.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been