Macro stops running randomly with no break or error when looping

Good day,

I am currently do the following:

1. Declare public variables
2. Run a sub Plot() which loops (11 times) and calls calls subs from other modules in order to plot graphs
eg Module1 and module2 which uses the public variables and plots graphs then calls Module 3 (also uses the public variable) then puts the graphs by copy pasting into a powerpoint presentation, saves and then closes it. I need to create 11 powerpoint presentations

I am getting many problems.

1. The code just stops with no error or break eg halfway through creating a powerpoint
2. If I run sub Plot() more than once consecutively it does not create all powerpoints. it justs opens the powerpoint (does not paste anything) then moves onto the next powerpoint without closing and saving the first etc...it does this 11 times.
3. If i close excel and open it sometimes runs correctly for loops 1 to 10. but stops halway whilst creating the last powerpoint.


I am not sure if its a memory problem, or a public variable issue. but its driving me insane!
Please help!

I hope this makes sense. Do I need to clarify anything?

Please help. This has been bugging me for over a month now and I cant seem to get past it!