I echo what Fruitbat says, many thanks for your time FT.
Lets see what happens in the patch today. If it is still the same I think my plan would be.
1. Produce a version of the same map without the F4 just to see if it is that.
2. If no improvement I will produce a map with no DML in case one of the scripts has broken DCS with too many checks/cycles etc (although exactly the same mission was run by Wingflyr on his server with seemingly no issues.)