Strobe Light Effect not working on text

I'm animating a HUD over video, and am applying a strobe effect to some text. However, it never strobes. At the default settings, the text stays on the screen. If I change the effect to "makes layer transparent" the layer stays transparent. this is over many seconds, even though the strobe duration is set to 0.5 seconds and the strobe period is set to 1.0 seconds. 

This is such basic stuff, and I've used this effect many times. What am I missing? I've screenshot the effect settings. (*note the warning sign is because this is an 8-bit effect in a 16-bit project This problem still occurs if I change the project settings to 8-bit).

Running AFX 23.6.0 on macOS 13.4.1 on apple silicon.