Thank you! Your list gave me an idea of what to check, and I found the culprit. I did assign app specific settings to Apple News so that I could use side back button to exit out of the news article back to the main feed. I checked the settings in Logi Options+, and noticed that the wheel button was set to "Change pointer speed". I went into Apple News and clicked the wheel button, and the mouse pointer changed back to the normal sane rate that I am used to. I guess that if you use app specific settings for toggles like changing the pointer speed, Logi Options+ remembers it when the app is running. Thanks for your suggestions because they gave me a path to find the solution. BTW, my mouse is connected to my MacBook via Bluetooth and only Bluetooth. I have no idea where the USB dongle is.