Timeout wating for grbl to idle

Hi I’m new to everything to do with GRBL and not a programmer
but have just built a 3 axis CNC machine using an UNO board and CNC SHIELD which worked great until recently
I’m now getting a message as follows :
timeout wating for grbl to idle during cancel incomplete
My stepper motors keep going for a while after releasing the jog key and even seem to make a second short run sometimes
Probably part of the same problem when I run the setup program to enable homing switches I get a message that I’m running at 30 khz and setup needs to run at least 33khz
I’m using the latest UGS NIGHTLY BUILD ( to my knowledge), all on WIN10 but I have also tried older versions of UGS too
I guess UGS configuration is stored somewhere on my computer as the layout on screen stays the same which I might need to delete to use a fresh new install as I’m sure I have accidently changed something I shouldn’t have
How can I resolve this ? any help is greatly appreciated and please in basic terms as I’m no Einstein
Regards, Alan