I have a very similiar problem, as yet unresolved.
Lets say I am running on 25% rapid, and have a tool change in the program. The machine will change tools, then take off at 100% rapid. It will execute the program until the next toolchange, but will hang up on m6 in the toolchange macro exactly as you describe. If it takes off with the wrong rapid rate, it hangs up EVERY single time.
I personally think it has something to do with being cold. I know that sounds crazy, but the only time mine does it is when it is fall or winter, and I didnt run the heat at night. Start machine up, it hangs up for about an hour then quits, and runs fine. I think is a bad connection somewhere, and when the control doesnt get both signals (in the ladder) it defaults to 100% rapid but cant tool cahnge because of the missing signal.
You said yours is getting worse, is it getting colder in your shop?
My dealer has looked at it twice, he added some more dwell time to the toolchange, might have helped some. It went several months without doing it, then 2 weeks ago, started again. I cant get my dealer to return any phone calls. I have an independant repairman coming Monday, if we figure it out I will definitly let you know.