I just looked at my library and that is the only series with this unique numbering "feature". Could be the new website or how that series is entered into the database. may need to be posted in the new website bugs
@akotsu Had the same problem. Customer assistance had me go to settings then on to Repair account. They were friendly and helpful. Chat wait time was quick. I think they had to remove the book from my account and resubmit from their end first before I had to go to settings.