It seems like there is an issue with the upgrade from Lemmy version 0.18.5 to 0.19.2 where the old login cookies are not accepted any longer and right now the only way to fix it is to manually delete the old cookies for slrpnk.net from your browser storage and log in again.

For Firefox: Settings > Privacy & Security > Manage Data... > Deleting Slrpnk.net

For Chrome: Settings > Privacy and Security > Third-party cookies > See all site data and permissions > Search for slrpnk.net > Click trashcan icon

For Edge: Settings > Cookies and site permissions > manage and delete cookies and site data > See all cookies and site data > Search for Slrpnk.net > Click little 'v' dropdown arrow > Click trashcan icon

Edit: the Lemmy devs identified the issue and it will require another bugfix release that will hopefully happed soon.