I use Lightroom regularly to export 450 images into 1080 video on my mac with no problem, 45 minutes approx.
In the last month and last update I have been unable to export a 45 minutes 450 images into 1080 video. I have cleared caches and increased the video cache to 60gb. I have restarted Lightroom many time and shutdown and restarted my mac. It will start to export but seem to stop as if a buffer is full. I can manage to export a very low quality video which gives me the idea a cache/buffer is limiting the action.
Any help would be great.
Lightroom version: CC 2015.6 [ 1078672 ]
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.11 
Application architecture: x64
Logical processor count: 8
Processor speed: 4.0 GHz
Built-in memory: 32,768.0 MB
Real memory available to Lightroom: 32,768.0 MB
Real memory used by Lightroom: 6,396.0 MB (19.5%)
Virtual memory used by Lightroom: 8,123.7 MB
Memory cache size: 763.2 MB
Maximum thread count used by Camera Raw: 8
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Displays: 1) 5120x2880
Graphics Processor Info:
AMD Radeon R9 M295X OpenGL Engine
Check OpenGL support: Passed
Vendor: ATI Technologies Inc.
Version: 4.1 ATI-1.42.11
Renderer: AMD Radeon R9 M295X OpenGL Engine