The issue is whether non-observance nullifies a conversion, and I have never seen a reasonable halakhic case made that a conversion can be annulled. A person who has brit milah and tevilah and verbally expresses their understanding of what is required of them is Jewish, period. This is how poskim have historically understood the matter, and the mishegoss I’ve seen in recent years is damaging and without any halakhic basis.
This is something to either laugh or cry about- a ger was converted by a former RCA president and leader in the Modern Orthodox community. The RCA itself doesn’t endorse it, and the ger went to a Chassidishe beis din in Boro Park (Biala, Satmar, and others) who accepted him without a problem and welcomed him into the Lvover shteible without issue.