Are there any other errors displayed or does restic just repeat that message over and over again? Is restic allowed to create and delete files in the locks folder of the repository? How many files does that folder contain right now (e.g. by counting the lines output by restic list locks)?
A failing lock refresh is problematic if any operation which might remove data from the repository runs concurrently. For example a prune run would normally abort immediately for a locked repository. But if the lock refresh does not work, it could run concurrently and cause data loss if you’re unlucky.