Being able to read but not write Kanji is so common that it's a meme amongst Japanese people -- to the point where it's a game. For example, here you can watch some Japanese television people play a game where they compete to write words in 10 seconds or less:
https://www.youtube.com/watch?v=pqQQqLno9hw
I (and every other learner) have the same problem. It's not special, and has nothing to do with aphantasia.