try some polyflex - like i said much more printer friendly than ninjaflex.
And if you do try ninjaflex - try green ninjaflex.
I had no problems printing that - but couldn't even get red nf to feed on the same machine.
Also had the same issues with filaflex - green - great. red, won't even feed.

Polyflex - on the other hand loads and prints just like normal pla. It's almost as flexible as ninjaflex - but less compressible.