How can I stabilize a souffle?
Try a small amount of cream of tartar instead of xanthan gum. Cheaper, more readily available, and the acid stabilizes the protein matrix.

Also, some tips from Better Homes and Gardens: use a collar, beat your egg whites to a stiff peak but remember to GENTLY fold them in, and don't open the oven door for at least 20-25 minutes to prevent cold air from collapsing the rising souffle.

And yes, even properly cooked souffles do deflate somewhat. Serve immediately and be gentle when removing from the hot oven - no banging the pan down onto the table.