That's a very good log, thanks. Unfortunately, it looks like you are running out of GPU memory, which would explain the freezes. Usually this indicates a memory leak or fragmentation; or you are just trying to allocate too much. The RPi3's GPU memory is not particularly large. You could try this script to see how the GPU memory consumption behaves over time: 
#57420
Do you experience these freezes when performing a certain action or just over time?
