As first reported here: How long is a "Learning Streak"? 365 days? - #34 by mike27827 there seems to be a discrepancy between the iOS and web displays for the same account.
I use an iPhone and iPad, my streak on iOS seems to reset occasionally even though it continues as per the website.
I don’t watch it closely so I don’t know when it happens, but have noticed it on several occasions. Right now it shows 53 on iOS and doesn’t increase when I do a day’s learning but it showed 89 on the website yesterday and went up to 90 today.
Website:
I have tried logging out, wiping and reinstalling the iOS version and still the same number comes back.