There is an Inspire poster that is fairly well known, PhoneyBoney. She was also fracturing on bisphosphonates etc.; I believe that she took various drugs.
She self reports that after taking strontium citrate that she stopped fracturing.
The links which I sent you has a 2020 compilation of strontium research; in that compilation the scientists say that one reason strontium has such a high success of preventing fractures is because it seems to make something called "sacrificial bonds" which allow the bone to sustain more injury.
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/dd823b-strontium-a-compilation-of-research-and-information/
I don't know if this sacrificial bond is what stopped PhoneBoney's bisphosphonate fracturing, but it is possible.
Strontium user stories:
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/strontium-users-stories-2-alternative-to-pharma-meds/