Don’t quote me on this (I could be horribly wrong). Voyager doesn’t seem to use cookies rather it relies on Index db and local storage. Local storage stores your credentials for your accounts (jwt tokens), and index db stores your preferences. If DDG only is preserving cookies and wiping the local storage and index db (again I haven’t tested DDG) then that would give a possible explanation on why you are getting logged out and potentially why any settings are getting reverted.
Edit article explaning difference between storage types:
Edit 2 It looks like ddg is clearing data and only preserving first party cookies (which isn’t used for voyager):
https://help.duckduckgo.com/duckduckgo-help-pages/privacy/web-tracking-protections/
It is planned but it probably will take a while to implement since lemmy doesn’t support webpush api. Without web push their are only two ways to check for notifications (both aren’t elegant):
Poll the lemmy api for new messages (say every min). This would be bandwith intensive for both voyager servers and your lemmy instance (Memmy does this and currently for 800 users 3gb of bandwith is used per day). Even if voyager is able to scale there servers to handle bandwith lemmy instances could impose rate limits which would prevent notifications from coming through.
Set up a weird janky system to intercept emails sent from lemmy instance to trigger a voyager server to ask the api if there are any new messages (would reduce poll rate but would be super clunky to setup).
Web push api could solve this issue since instead of voyager having to ask lemmy if their are new messages web push allows the opposite to happen (lemmy telling voyager a new message has arived).
https://github.com/LemmyNet/lemmy/issues/3552