Modal animation not working in HM2024

I've done a modal analysis in HM 2024 (OptiStruct), and everything seemed to work OK, but when I use the the animation tools, I can't seem to get the desired animation of the mode shape. I have it set to modal, and it goes from zero to max displacement and then back to zero and repeats. I can't seem to get it to cycle between positive and negative displacements as it should. I'm probably missing something obvious, but I feel like I've tried every permutation of options. (I used to have no problem with this in the 2021 version).