Retraction distance to great, try reducing it a bit at a time, but change nothing but that each time so as to know if it working.
If that does not do it and you are using S3D, add some Extra Restart Distance.. When retraction pulls the filament back x number of MM it will then advance it the same amount when it gets to where it is going. Sometime you need a little.. that is what extra restart distance is.. Don't add too much to start and work up to what is required.
Good luck