TestComplete/Execute process not closing automatically

Funny you mention mutex. 

Is this a virtual machine? Like is your box running 4 VMs, in turn running multiple TestCompletes?

Is it possible that your box does not have 4 cores, thus running into mutex locks? Note I'm just using an arbitrary number. It's possible you're running 16 VMs using only 4 CPUs.

Try putting a random delay in each batch file. 

https://stackoverflow.com/questions/34524/what-is-a-mutex