Hello @Jake_Blumenthal welcome to Zwift forums and Zwift more generally!
Shuji at Zwift HQ here. I looked through your server log history and noticed that you have logged in from both a PC and an iPhone 9. When you’re logged in from two different devices, weird symptoms occur - activities not saving to your activity history is one of them.
Is the PC your preferred device to run the main app? To avoid the concurrent logins problem completely - we recommend you uninstall the Zwift main app from the iPhone.
If the iPhone is your preferred device, then uninstall from the PC. Additionally for mobile users - it is important to always save-and-exit (or trash-and-exit) every Zwift session. This will tell the server affirmatively that you intend to end your session. If you don’t, and leave the main app running in the background on your iPhone - this can also result in your activities not showing up.
Hope those help!