Nope, I do not share my runemate account. I do have other runemate accounts that are inactive and abandoned secondary to losing phones and losing two-step verification access. However, these have been inactive for months/years so should not influence my total hours.
There have been several instances during the time period in question (Feb 11-12) where Runemate has updated, but my instance has continued to run up until that instance was either manually stopped or completed. Could that have triggered some kind of bug?
EDIT: what confuses me still is that I only have ONE instance running at any given time, and I seem to have used 49 hours within a 24 hour period.