Definitely seen it before, but only a rare handful of times. Related: Certificate issuing problems with Caddy, Proxmox VE while ISP is blocking port :80 - #6 by Whitestrake
Nothing to do but blow away the bad ACME account files. Making a fresh one isn’t an issue as long as it doesn’t happen too often, but this is not a common issue at all as far as I can tell. Would’ve been curious to know how they went bad, for sure.