Since your post is somewhat recent, I would love to hear how you are progressing over the last 11 months. I stumbled on this thread in a very similar fashion, i'm having high oxalate issues after mega dosing both Vit C and collagen powder. (Also d-mannose, this apparently converts to oxalate too in high amounts)
I "know" I have an oxalate issue. While reading through this thread, I became very convinced that the original poster's issue looked oxalate related and was nearly going to post a message similar to yours. I arrived here by searching for MSM & Oxalates after reading up on a methylation article.
Has MSM been helping you? or have you made other progress and learnings related to your oxalate issue?