If the algorithm switched you to another cycle but you didn’t log a period, it's most likely due to the fact that you haven’t been logging any data recently.
If you don’t log data in the app, the algorithm will switch you to another cycle once you pass your predicted period. As a precaution, the new cycle will start on the day you usually get your first Red Day. For instance, if you usually get Red Days starting from Cycle Day 6 (CD6), the new cycle will start from CD6.
This is a safety measure; as the algorithm can’t guess what happened while you were not logging data, it allows the algorithm to exclude the ‘incomplete’ cycles from influencing your future predictions.
If this happens, you can easily fix it by merging the two cycles. To do so, select a day before the cycle switch and log some data on that day (such as a mood, etc). This will let the algorithm know that you’re still using the app and it will merge the two incomplete cycles into one valid cycle.