Can't login to Plex any more

[Karmalakas]

A few days ago I noticed it stopped syncing my watch history. Tried a bunch of things but nothing helped. Found issue already logged where second user also got logged out, but in my case it's main user - second user is still connected and fine. After I enter PIN on Plex, I see this block refreshed and my avatar shown, but then later it again asks to enter PIN on Plex. After I enter PIN on Plex, I see these requests in console with these responses:

https://plex.tv/pins/xxx.xml

<?xml version="1.0" encoding="UTF-8"?>
<pin>
  <expires-at type="dateTime">2021-11-24T16:34:29Z</expires-at>
  <id type="integer">[number]</id>
  <code>[PIN]</code>
  <user-id type="integer">[xxx]</user-id>
  <client-identifier>[xxx]</client-identifier>
  <trusted type="boolean">false</trusted>
  <auth-token>[yyy]</auth-token>
  <auth_token>[yyy]</auth_token>
</pin>

expires-at matches exact time the request was made

And then https://plex.tv/users/account

<?xml version="1.0" encoding="UTF-8"?>
<user email="xxx" id="xxx" uuid="xxx" mailing_list_status="active" thumb="https://plex.tv/users/xxx/avatar?c=xxx" username="xxx" title="xxx" cloudSyncDevice="" locale="" authenticationToken="yyy" authToken="yyy" scrobbleTypes="" restricted="0" home="0" guest="0" queueEmail="[email protected]" queueUid="" hasPassword="true" homeSize="1" maxHomeSize="15" secure="1" certificateVersion="3">
  <subscription active="1" status="Active" plan="lifetime">
    <feature id="webhooks"/>
    <feature id="content_filter"/>
    <...>
    <feature id="ad-countdown-timer"/>
  </subscription>
  <roles>
    <role id="plexpass"/>
  </roles>
  <entitlements all="1">
    <entitlement id="roku"/>
    <entitlement id="android"/>
    <entitlement id="xbox_one"/>
    <entitlement id="xbox_360"/>
    <entitlement id="windows"/>
    <entitlement id="windows_phone"/>
    <entitlement id="ios"/>
  </entitlements>
  <profile_settings default_audio_language="en" default_subtitle_language="lt" auto_select_subtitle="0" auto_select_audio="1" default_subtitle_accessibility="3" default_subtitle_forced="2"/>
  <services>
    <service identifier="epg" endpoint="https://epg.provider.plex.tv" token="xxx=" status="online"/>
    <...>
    <service identifier="lyricfind-search" endpoint="https://lyricfind.plex.tv/" token="xxx" status="online"/>
    <service identifier="tvdb" endpoint="https://api4.thetvdb.com/" token="xxx" status="online"/>
  </services>
  <username>xxx</username>
  <email>[email protected]</email>
  <joined-at type="datetime">2014-02-22 08:02:33 UTC</joined-at>
  <authentication-token>xxx</authentication-token>
</user>