Strange site effect caused by a missing cookie?

[FunSniper]

For about a week now i have a slight annoyance: sometimes after a new page of a story is loaded the site reverts from dark mode back to default and offers on the top to log in or register.
I literally see the dark page for a second or two before this happens and after refreshing the page with [F5], it goes back to dark and logged in and stays that way while i read that page, but it might trigger again on the next page.
The only hint i found while the site wasn't properly loaded was following message found via [F12 -> Console]:
Cookie “enable_beta_story” does not have a proper “SameSite” attribute value. Soon, cookies without the “SameSite” attribute or with an invalid value will be treated as “Lax”. This means that the cookie will no longer be sent in third-party contexts. If your application depends on this cookie being available in such contexts, please add the “SameSite=None“ attribute to it. To know more about the “SameSite“ attribute, read https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cookie/SameSite
common-600378d38a0b1d513bd9.modern.js:1:236587

Via [F12 -> Storage -> Coolies], no cookie with that name is listed.
Over the link offered to view the code in the Debugger i could identify a piece about that cookie and the position offered pointed to a variable. (Lost me there as i'm not a JS-Dev, i just know a bit about reading code)

OS: Devuan Daedalus 5 stable 64Bit
Browser: Waterfox G6.0.13
Site where this was found: [One Who Understands, page 25 onwards]
Sites where this didn't happened: [Quaranteam Ch 1-10, any page] [Bait and Switch Retype - Complete, tested up to page 26]
(Stories selected as they have more than 2-3 pages and one is older (2013) and one is newer (2021) as the story i found this issue (2015))
Last update: was made a few week ago, i think

 

[Britva415]

You should probably just delete all the site-specific cookies so that the site will re-set them properly for you. You seem like you know or can easily figure out how to do that.

 

[FunSniper]

You should probably just delete all the site-specific cookies so that the site will re-set them properly for you. You seem like you know or can easily figure out how to do that.

Nope, deleting them multiple times didn't change anything.

But I might have found why the cookie was never set:
In Control Panel -> Options -> My Options there is a point "Participate in early site feature versions beta-testing" that looked like it was set to yes (should have been automagically, i think).
Turned it of an on again and now that cookie was created and can be found in [F12 -> Storage -> Cookies].
Seems by not changing that ever the state was somehow undefined as i saw and used new features and at the same time the cookie was never set.

EDIT:
And again the same message after the story-page turned white again. Only: this time the cookie exists and is reported to expire in about a year.
relevant data (date-fields omitted):

Domain:".literotica.com"
HostOnly:false
HttpOnly:true
Path:"/"
SameSite:"None"
Secure:true

EDIT2: Tried to manually set HttpOnly to false and saw the cookie has vanished after getting another light-mode page...
I'm tempted to force a CSS via Violentmonkey, knowing it might break things...