The session glitch is a mysterious glitch that affects certain sessions of the game. It is connected to the arrival of Lrd English within a universe. So far, all that is known about the glitch is what Doc Scratch .
In a normal (unscratched) session, the players create paradox clones of themselves and their guardians through ectobiology who go back in time to the point of their respective "births" through Skaia's defense portals during the Reckoning. If the players scratch their session, the paradox clones of the players and their guardians are sent to opposite points in time by Skaia when they pass through its defense portals, creating a new timeline (e.g. the kids switched places in the post-scratch version of Universe B, where the guardians became the players, and the players became the guardians). Thus in a post-scratch session no ectobiology lab exists within the veil or occurs at any point, a paradox sanctioned by the action of the Scratch.
This arrangement is violated in session suffering from the glitch. The players find no ectobiology equipment in the veil, and/or by whatever means or for whatever reason are incapable of performing the ectobiology necessary for their and their ancestor's existence. The only plausible explanation is that they originate from the other side of a scratch. Ergo, the players have no choice but to deliberaly fail their session and scratch it, lest they doom the timeline.
The glitch works by triggering "an unfathomable cascade of misfortune throughout Paradox space". Glitched sessions are highly Null and entirely unwinnable; a group of players in such a session are said to suffer a failure "more comprehensive and systemic than the simple inadequacy so common to young players of this game". The players' only option, besides accepting absolute defeat, is to initiate a scratch and reset their universe. This is inevitable from the start, due to the fact that the scratched universe is necessary for their own creation.
The glitch is stated to be the "calling card" of Lrd English, and is the way he "reserves his place in a universe for later visitation". It is implied that the scratching of a glitched session is specifically what allows Doc Scratch to become the First Guardian of the player's planet in the reset timeline. This is how Lrd English enters the universe, using Doc Scratch as an excellent host.