Recording in incognito mode is highly discouraged. Under normal circumstances, your session will record and upload without problems. However, incognito mode prevents the saving of local backups of each participant's local tracks. If there is a problem with the upload, it will be impossible to recover the audio from the local backup.
If you see a notification that your guest is low on disk space, it may be an indication that they are using incognito mode as it only reports a very small amount of space as available. In this case, it is a good practice to ask your guest if they are in incognito mode and have them switch to regular browsing mode.
We are working on trying to accurately detect incognito mode so we can warn hosts before the recording starts but it is difficult by design. Otherwise, it wouldn't be very 'incognito'.