My humble understanding is that tymlos 'pushes - forces' the osteoblasts to build bone. After 16/18/22 months these cells do not respond as well to the medication. The osteoclasts are ramped up to 'dismantle bone' and this makes the 'bone coupling' ( 'building' compared to 'dismantling') out of sync.
Hopefully you have been keeping track of P1NP and CTX- bone markers. The 'bone building' rates can be checked thru bone makers ( P1NP ). When this result starts to wane compared to your history, then the medication is losing effectiveness. Tymlos is then stopped; a medication is given immediately for a short time to maintain the gains. Do not skip this step. I repeat do not skip this step. TYmlos was just apporved to be given again - how effective this is depends on many issues including bone markers and dexa and tbs. Make sure your endo is a BONE specialist. May you get good guidance and restore your bones to strenght and vitality.