We had a *very* weird bug, almost impossible to locate and we still do not know the *exact* reason. It had to to do with the Memory protection unit.
With the file above, so far all the 1.7 sec freezes got fixed.
I have also been modifying the TSynth code and saw this problem at one point. I'll share some details in case it gives you any additional clues.
When using a std::vector collection of pointers I experienced the freeze/beep while using range-based for loops, the problem stopped if I accessed the values directly by index. Inside the loop I was modifying frequencies, gain, envelope states, etc.
Now that I've found this thread I tried to go back and reproduce the problem so that I could verify the 1.54 Beta 7 fix. Unfortunately I'm no longer able to reproduce the issue so cannot verify the fix.