The problem in the case of galaxy AGC 114905 is(see this) is dcussed in a popular article "In a Wild Twist, Physicists Have Revived an Alternative Theory of Gravity" published in Science-Astronomy (this). This galaxy is of the same size as Milky Way and seems to have very small amount of dark matter, if any.
Mancera Pina et al (see this)argue that both cold dark matter scenario and MOND fail to explain the anomalously low value of the rotation velocity of distant stars. The proposal of Banik et al (see this) is that the inclination between the galactic disc and skyplane is overestimated, which leads to a too small estimate for the estimate for the rotation velocity so that MOND could be saved.
In the TGD framework (see this, this, and this), the rotation velocity is proportional to the square root of the product GT, where T is the string tension of a long magnetic flux tube formed from a cosmic string carrying dark energy and possibly also matter. In the ordinary situation, the flux tube would be considerably thickened only in a tangle associated with the galaxy as part of volume- and magnetic energies would have decayed to ordinary matter, in analogy with the decay of inflaton field.
If the flux tube itself has a very long thickened portion such that ordinary matter has left this region by free helical motion along the string or by gravitational attraction of some other object, the string tension T is small and very small velocity is possible. Ordinary bound state of matter is not necessary since the gravitational force of the flux tubes binds the stars. This might explain why the galaxy can be ultradiffuse.
For a summary of earlier postings see Latest progress in TGD.