This method uses NDI and OBS as a bridge between Premiere Pro.
With a non-standard sequence resolution like 1080 x 1080 (1:1) or 900 x 1080 (5:6), Premiere will attempt to output exactly that resolution to the Blackmagic Decklick or UltraStudio Monitor device.
However, Blackmagic's monitoring devices are SMPTE-compliant and only output standard formats like e.g. 1080p25 (1920 x 1080).