Yes, my guess of what is going on exactly is that these regions from the wear-and-tear of life are inflamed and needing more iron (and folic) to repair and we are giving it the iron (and folic) each dose, which they’re accommodating in brilliantly but just then not getting enough of the accommodating niacin (given iron dose was too high) to finish the job each dose, leaving say these tendons signaling “hey I still need more niacin to finish this inflammation/debris clearance but it’s suddenly gone,” and so this is what you literally feel. Relaxing relative mass of iron to what it is now should provide enough niacin calibrated to iron (and folic) to better finish the job now and thus not feel any sensation.

https://pubmed.ncbi.nlm.nih.gov/16276022/

“Taken together, our results suggest that iron accumulation in the weeks after inflammatory demyelination may contribute to lesion repair rather than inflammatory demyelination per se”

Potential role of iron in repair of inflammatory demyelinating lesions

https://www.jci.org/articles/view/126809

Give the new relative mass ratios a few days of dosing, and if this happens again because iron (or folic) is still too high or even weighing out too much by accident unknowingly, then simply hit a niacin solo dose of at least 1.5 g or so to finish the anti-inflammatory & debris clearance right then