I would say ill fitting shoes/boots.
I wear safety boots for work everyday. I walk an average of 16miles a day in them and had no problems.
But... unfortunately the boots my company supply are cheap and nasty. And just don’t fit me. I also have tiny feet (uk size 4). There supplier only does boots down to a size 5.
So therefore I buy my own, and my employer reimbursed me upto £35. Some others (non diabetics) found the boots fit badly and caused them problems, and as as we have to have them to work, HR authorities this for them to! I didn’t need the note as they can’t provide me size.
But worth looking into!