[CitizenOfDreams]

It seems that some USB boards have issues with probing. Here is a thread about a similar problem:

G31 Probe SOMETIMES works (Mach3 USB) (SOLVED) - AutoLeveller

[ZeroBacklash]

It seems that some USB boards have issues with probing. Here is a thread about a similar problem:

G31 Probe SOMETIMES works (Mach3 USB) (SOLVED) - AutoLeveller

Thanks for the link, the OP in that post seemed to have solved his problem with another version of Mach3. So I don't know how much it has to do with a USB controller. I have a chinese controller though.

[ZeroBacklash]

It seems that some USB boards have issues with probing. Here is a thread about a similar problem:

G31 Probe SOMETIMES works (Mach3 USB) (SOLVED) - AutoLeveller

OK, to anyone who has this problem.
CitizensOfDream was right it seems to be a problem related to certain USB controllers.

So the solution is in this thread

Aircuts on Mach3 USB NcUsbPod - AutoLeveller

There are a number of solutions presented over there.
By "steamer" however I directly tried the solution posted by user "Renato" where he added a dwell time before the G31 probing command

like this

G4 P1
G31 Z-5 F100

So following this I just did a find and replace of the probing lines.

In addition I changed the probing depth from -1 to -5 as shown. so instead of G31 Z-1 F100 I used G31 Z-5 F100

Hope this helps.

Many thanks "CitizenOfDream" for your advice its highly appreciated.