Problems with mach3 and cslabs controller - jittering & losing connection frequently.

I know I haven’t posted for a while, but my machine has been working fine, and life has been busy.
I have a developing problem, sometimes the machine jitters like it’s catching up with data, other times more commonly mach3 loses connection with cslabs and it stops mid cut. I am using stepper motors. The jittering occurs on large complex 3d NC programs, mach3 losing connection is random when it occurs.

I am using a windows xp laptop and connecting via an Ethernet cat 6 cable. At first I thought it was the Ethernet ports - poor connections. So I replaced my interfaces with the machine with screw down Ethernet connects made by Neutrik for microphones etc, also a new cable which is shielded ( last on was to) The problem hasn’t gone away.

I cannot seen to find much information online about setting to tweak. Most popular suggestion was to use cslabs interface instead of mach 3.
I have rebooted my laptop a few times and cleaned all the contacts in the data path, so I am now not sure what to look at next. I haven’t changed any of the settings from those Dean helped me put in 9 years ago.
Any tips to resolve this would be appreciated