Hi Grace,
Thanks for reaching us. This shouldn't be happening!
Since when are you encountering this issue? Could you try working on a different or incognito/private browser mode on the iMac? Would it be possible for you to try after connecting the iMac to another network? Also, could you try sharing the project within your work network to see if it is limited to just this device/network?
You may try disabling browser extensions/plugins. You may even try after clearing the cache/cookies of your browser.
Let us know about your observations; we are here to help just need some more info.
Regards,
Amitej