Program occasionally starts running at double speed?

I’m running PTB on MATLAB R2021 on Windows 10.
My program is a visual perception experiment with dichoptic presentation on 2 different monitors, moving stimuli and eye-tracking. Every so often when I open a PTB window the program runs twice as fast (stimuli move twice as fast, half length trials). This happens unpredictably, so only every few experiment runs, and it’s not really reproducible. To deal with it the only thing I can do is close the program and restart it. I use different PsychImaging configurations for Eyelink calibration (‘MirrorDisplayto2ndOutputHead’ with a default window on the main monitor) and for stimulus presentation (mode 10 for stereo presentation), so every 6 trials I close the stimulus presentation window, open a new one, do drift correction, then open a new stimulus presentation window. I think something about opening a window might be causing it. It’s really a pain to account for this bug in analysis. Does anyone have some idea what could be causing it? My stimuli are refreshed at 60 hz, the maximum refresh rate of the monitor.

That’s a new one. The best advice is always to switch to Linux for anything that requires reliable multi-display, MS-Windows is often a troublemaker.

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