On desktop, my session is usually pretty stable; I only see myself logged out on domains I'm not active on, like mathoverflow.com. However, twice so far today (over a span of no more than 2 hours), I've been logged out of SE entirely. The first time triggered the dark mode bug. The second time was in the middle of a chat conversation and resulted in my message suddenly giving an error instead of sending.
Given the maintenance last night, I'm wondering if this is a widespread problem.
CookieTokenDoesNotMatch("account session was deemed invalid"). I'm not sure what would contribute to your token no longer matching, but just wanted to clarify that this is not related to the recent maintenance - all that changed was the location of the OpenID database, and the database is only touched on initial authentication anyway (so even if the database disappeared mid-session, it wouldn't affect you, for the same reason relevant maintenance windows don't impact existing active sessions).