Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
If it's just on the edges of the squeegees that you see the chatter marks, it's an easy fix- round your squeegee corners. Also, top tape your squeegee drop/finish areas as well as the very edge where the sq corner hit the emulsion.If the chatter marks are inside the image area it's just a matter of your blade/pressure/substrate/# of impressions/off contact, etc. being too much for the emulsion. SP1400 is tough chit from what I hear but 6k impressions will start to get at most any emulsion, just a matter of friction over time. You can combat break down inside the image area by face coating the ink side of the screen, putting a little more emulsion on there to resist the wear/tear.But really, rounding the corners and top taping will solve most of this. Good luck!
We run the PHU and have had the "cracking" in the past. At least for us when it gets cold and dry (winter) I cut my exposure time down about 10 ltu across the board, it seams to help and I have not had any screens break down.