Only the Support can check that, so you may want to raise a bug ticket here.

However, I do have a possible explanation: when you say "[I] have never missed a day playing", are you sure you logged in on every server day? Time zones matter here, and the server is running on UTC (as it should). The reset happens at midnight UTC.

So, if you are - for example - in California (I picked it randomly), your time is currently UTC-7:00. In that case, daily resets happen at 17:00. Now, if you log in on the game at 16:00 one day and at 18:00 the next day, two resets have happened without you logging in and you've missed a (server) day.

I don't know if this applies to you. It's just a possible explanation, but only you know if that's what has happened a week ago or not.

P.S. Not that it matters, but s2 was moved from Kabam to Plarium portan on 2017-02-20, and our prestige was reset to zero then, so - even without losing a day - your prestige would've been 1333.