Since upgrading to Version 5, I have still been receiving this audible click error at the start of mixdowns. I have completed some tests and regardless of if I have Ampire in the session or not, the issue was ongoing.
I just did a test and if I have both my device and processing block size on their maximum settings (4096 samples) and choose "Use Realtime Processing" instead of my usual offline mixdown, this issue is resolved.
I can only conclude at least in my situation that this issue was tied to the offline export feature.
If anyone else has success with the above troubleshooting for this issue, let us know in this thread.