Kdenlive suddenly slow when render

Hi!
I installed Ubuntu gnome 16.04 recently and I use Kdenlive to edit video files. I really like the program and I have been using it with both kubuntu 15.10 and debian 8.4.
The videos I usually work with are 30/40 minutes long and I usually render them to mpg witch takes 30 - 50 minutes using 4 of the CPU:s 8 cores. Now is suddenly 2 hours and 30 minutes!! What happened?

The difference from before that could has something to do with it is that I changed my GPU. I had a radeon r9 390 when it took 40 minutes and now I have a radeon R9 fury X. But this card is supposed to be better.
Any ideas?

I'm ruing the 4.15 version of Kdenlive