Weird. The series that appeared to have been reset on me were The Tyrant Falls in Love and Futari Monologue, and since their total values had been the only obvious thing that changed recently I thought that was what was responsible.
That said, is that data stored client-side or server-side? If it's the former, maybe something like an improper browser shutdown or something was to blame instead.
Edit (27th June 2019): The Peerless Concubine has also had its numbers reset to 0 on me, and yet its numbers have not been updated from ? (that I can see, unless they were modified and then changed back).
Edit (30th June 2019): Level 1 Dakedo Unique Skill de Saikyou desu on my end has also been affected. Is there a hard cap on how many series' reading progress each user can actually keep track of...?