Yesterday evening (around 23:00 CEST I think) all my normal reviews (i.e. excluding ghosts) were pushed back by a month for some reason. I still have a cached page load of my profile page from before that which shows all items under “Show Upcoming Grammar” had a next review time between a few hours and 2 months, but now everything (except for the 5 grammar points I added this morning) is due in either 1, 2 or 3 months. The stats page still shows many items with a streak of less than 1 month, so it’s only the time for the next review that changed, not the actual streak.
A bit before this I got an email confirming my purchase of a monthly subscription for the second time (the first one was a month ago, after the actual purchase). Might be related? (Unless you actually just send these confirmations every month, it’s only my second month of paying so I wouldn’t know. Also, I use different emails for Bunpro and PayPal. As this required you to change something after the first payment this might be the reason why your system considered this second payment to be my first…)