We present new HI interferometric observations of the gas-rich ultra-diffusegalaxy AGC 114905, which previous work, based on low-resolution data,identified as an outlier of the baryonic Tully-Fisher relation. The newobservations, at a spatial resolution $\sim 2.5$ times higher than before,reveal a regular HI disc rotating at about 23 km/s. Our kinematic parameters,recovered with a robust 3D kinematic modelling fitting technique, show that theflat part of the rotation curve is reached. Intriguingly, the rotation curvecan be explained almost entirely by the baryonic mass distribution alone. Weshow that a standard cold dark matter halo that follows the concentration-halomass relation fails to reproduce the amplitude of the rotation curve by a largemargin. Only a halo with an extremely (and arguably unfeasible) lowconcentration reaches agreement with the data. We also find that the rotationcurve of AGC 114905 deviates strongly from the predictions of ModifiedNewtonian dynamics. The inclination of the galaxy, which is measuredindependently from our modelling, remains the largest uncertainty in ouranalysis, but the associated errors are not large enough to reconcile thegalaxy with the expectations of cold dark matter or Modified Newtoniandynamics.

We quantify the relative importance of environmental quenching versuspre-processing in $z\sim1$ clusters by analysing the infalling galaxypopulation in the outskirts of 15 galaxy clusters at $0.8<z<1.4$ drawn from theGOGREEN and GCLASS surveys. We find significant differences between theinfalling galaxies and a control sample; in particular, an excess of massivequiescent galaxies in the infalling region. These massive infalling galaxieslikely reside in larger dark matter haloes than similar-mass control galaxiesbecause they have twice as many satellite galaxies. Furthermore, thesesatellite galaxies are distributed in an NFW profile with a larger scale radiuscompared to the satellites of the control galaxies. Based on these findings, weconclude that it may not be appropriate to use 'field' galaxies as a substitutefor infalling pre-cluster galaxies when calculating the efficiency and massdependency of environmental quenching in high redshift clusters. By comparingthe quiescent fraction of infalling galaxies at $1<R/R_{200}<3$ to the clustersample ($R/R_{200}<1$) we find that almost all quiescent galaxies with masses$>10^{11}M_{\odot}$ were quenched prior to infall, whilst up to half of lowermass galaxies were environmentally quenched after passing the virial radius.This means most of the massive quiescent galaxies in $z\sim1$ clusters wereself-quenched or pre-processed prior to infall.