AAX cpu overload dialog box on first playback only

I am using PT 12.5.0x71 developer app, mac 10.13, latest JUCE. I have been using and testing my plugin for a long time and I would get the occasional cpu overload dialog (error -6101), and yet I do not do anything cpu intensive. So, I wanted to reorganize my code and get to the bottom of these issues. After reorganizing, I get a cpu overload dialog on first playback through my plugin 100% of the time. Thereafter, I never get a cpu overload. Note, AAX starts streaming audio as soon as the plugin is inserted…no issues there…then I start playback and get the cpu overload dialog…then I start/stop playback as many times as I want after that and there is no issue.

I thought maybe I was allocating some memory in the real time code path, but can’t find anything. I timestamped the processBlock function and it never takes more than 1ms. Since AAX just presents a dialog for cpu overload, I have no stack trace or anything to help me identify what is triggering that dialog. I don’t even know if the problem is in processBlock. Any ideas?