when searching on taxon in the Android app, i find that it’s better (more reliable) to search using the Explore page than using the (universal) search in the My Observations page, even when searching only for my own observations.
i would guess that the way the search on the My Observations page is working is likely intentional so that, for example, a search for “dog” doesn’t return observations of dogwoods.
when you use the taxon-specific autocomplete in the Explore page, you usually won’t have to type the whole taxon name to be able to select it for your taxon filter.