I've lost my big toe toenails more than once and one of the things you mentioned stuck out. You've been wearing the same shoes for several years. Unfortunatley our feet do tend to get larger as we age; not necessarily longer, but a little wider which means needing more space in the shoe for those times we have swelling.

So, next time you buy new bike shoes, try several pair on and go with comfort versus the size you've always worn in the past and, keep those toenails clipped.