There are a couple odd issues when you fullscreen the app on a multi-monitor setup in macos.
If you move between windows while in fullscreen the resolution doesn't update so you have a tiny window. Toggling fullscreen fixes this.
If you lost the second monitor while the app is fullscreened it will stick it overtop whatever is on the other monitor in fullscreen and you have to toggle fullscreen to fix it.
There are a couple odd issues when you fullscreen the app on a multi-monitor setup in macos.