Streak number is hugely different on app vs website
I've posted about this before, but on my app the streak number is about 12 days where its well over 200 on the website.
If you've posted this before, I'm probably just going to give you the same answer you've already seen.
My guess is that the app is showing you 'language' streak (this is your streak for each individual language, and a streak freeze does not affect it). The streak on the website is your 'overall' streak. This is your streak for all languages studied and is the streak frozen when you use a streak freeze.
Have you updated your app? I thought they had fixed this problem with an update, but maybe not.