There is the list of cubesats, including cancelled and planned, that looks much more full than ones in Wikipedia. Two Dragracer cubesats of size 2x2x1.5U are mentioned near the end of this list. These planned to launch in 2020 on board of Electron KS launcher. It looks like that size of 2x2U was simply skipped (and is awaiting for it realization).
Dragracer is mission to demostrate electrodynamic deorbiting of satellites to show, that a small satellite with a deployable tether can safely deorbit in a matter of weeks.
The Dragracer project is a joint project to test Tethers Unlimited's Terminator Tape, a conductive tape designed to produce enough drag to lower the satellite's orbit. Millenium Space provides the bus, integration is provided by TriSept and launch by Rocket Lab.
The mission consists of two basically identical satellites 6U (2×2×1.5U) CubeSats of a joint weight of 25 kg. The satellite with the terminator tape is called Alchemy, while the reference satellite is called Augury. After deployment, the two spacecraft split up and one deploys the 70 m Terminator tether, while the other one decays naturally to provide a direct comparisson. It is expected, that the satellite with Terminator Tape will reenter after about two to four weeks, while the other will remain about eight months in orbit. Millennium will use radar to track the satellites and collect data.
Also is mentioned that 2x2x1.5U is the Raptor class bus, and mass of each cubesat is 12.5 kg. Orbit is planned about 400 km high.
Image from here.
UPD: Another "square" cubesat with dimensions of 3x3U is ULTP, launched 7 March 2020 on board of Cygnus NG-13 cargo ship inside of Slingshot deployer. Orbit after deploying was 476 x 486 km with inclination of 51.65 degrees. Mass of ULTP is mentioned of 25 kg, that looks too much for 9U. For 3x3x1 dimensions it is unclear is it 300x340.5x100 mm or 300x300x113.5 mm, according to Cal Poly San Luis Obispo cubesat design specification.
Also, it is unclear geometrical size of Dragracer - is it 200x200x170.2 mm or 200x227x150 mm, although 150 mm is not mentioned in Cal Poly SLO specification (it looks like 200x200 on the picture). Of course, some subesats may not comply with this specification, there are examples of 1U cubesats (excuse me, I lost the links), that slightly more than 100x100x113.5 mm. It depends of cubesat deploying method.