I recently upgraded from Anki 2.1.35 to 2.1.49 running on Arch Linux. I am not using any addons.
As soon as I did that, every card gets reset to an interval of 1 day as soon as I study it, regardless of the previous state of the card. “1d” is shown as the interval for all rating options, even for the “again” button, which is really strange.