If one tries to add a project with observations fields, it appears to be limited to only a single project on the Android phone. Additional projects load, but their observation fields cannot be accessed for entry.
The iPhone behaves correctly in this regard.
Tested on several phones, at CREW outing on 18 May.
For projects: https://www.inaturalist.org/projects/crew-site-sheet-s-afr; https://www.inaturalist.org/projects/crew-species-sheet-s-afr; https://www.inaturalist.org/projects/habitats-s-afr
(see data collected here: https://www.inaturalist.org/observation_fields/10513)