this is normal biological adaptation, not failure
However, current evidence is primarily derived from in vitro models or animal studies, and often relies on indirect indicators such as protein expression changes (e.g., LC3-II, Beclin-1)
(I am a big advocate of spacing out doses for people who have reached their goal weight, OR who are taking GLP-1s primarily for a possible metabolic/anti-inflammatory benefit, and who want to keep their weight neutral.) But maintenance dosing after achieving a clinical response is a completely different concept from starting at a sub-therapeutic dose and hoping it works
Neither is categorically better
The more pronounced decline in hip BMD, as compared to the relative preservation of lumbar spine BMD, is likely due to the predominance of mechanically responsive cortical bone in the hip, whereas the lumbar spine is composed largely of metabolically active trabecular bone