It’s probably because you had a lot of exposure but insufficient engagement. I should probably have mentioned this in my original comment. You kind of developed a one way mastery of the language. Exposure will get you there after you get to a certain level but to get there you need lots of practice
Lovely. I used to have a Ukrainian coworker and she overheard me use the word ‘zoeken’ (search) and she thought I was swearing as I didn’t pronounce the ‘n’ strongly