Very slow export on clips with speedup

Hello,
I've been grading a timeline imported from FCP that has clips with changed speeds. All source footage is ProRes422HQ. Some of the clips are 4x the original speed, others have different speed settings.
The timeline plays back fine. When I render out though, the render slows down to a crawl (1 frame per minute) once it gets a couple of seconds into one of those clips with big speed changes.
I've tried to change the render speed to 5 and to use "cached" clips, but the render still slows down.
I'm on OSX with a GTX1060 3GB card. I've upgraded to the newest CUDA, and also tried to switch to OpenCL, but the problem persists.
I'm thankful for any tips.
thanks
yp
I've been grading a timeline imported from FCP that has clips with changed speeds. All source footage is ProRes422HQ. Some of the clips are 4x the original speed, others have different speed settings.
The timeline plays back fine. When I render out though, the render slows down to a crawl (1 frame per minute) once it gets a couple of seconds into one of those clips with big speed changes.
I've tried to change the render speed to 5 and to use "cached" clips, but the render still slows down.
I'm on OSX with a GTX1060 3GB card. I've upgraded to the newest CUDA, and also tried to switch to OpenCL, but the problem persists.
I'm thankful for any tips.
thanks
yp