One could assume that they were built by the Dronomeks trapped in the underbelly of Orcelot Rex's ship from the End Game comic. They are obviously newer more ‘Absolution II ’-ish type versions of they’re former selves (Clyde 50s and Clyde 49) as they carried out the same tasks as the previous Clydes. Their tech matches their surroundings and further suggests they were assembled along with the Absolution two, rather then TOM creating them post-occupation.
Jeff Harris of The X Bridge said it best, the Clyde 51s are essentially "Living Emoticons". They can display their moods and react to a situation directly on their screen as they have simple faces on them. They more or less complete the same tasks as the previous Clydes such as flying around, harassing each other, helping out where they’re needed and providing subtle comic relief.
These Clydes were phased out and replaced with Clyde 53s when Toonami switched to Saturday nights. However, they make a cameo appearance in Cartoon Network Universe: Fusionfall. If it coincides with the Toonami canon, it may serve an explanation for their absence.