In a recognition type of card, there is a hiragana at the backside of the card, instead of the kanji I put. I added this card in Android at first, noticed the error, then edited it on desktop (Linux), but the problem persisted. The picture explains my problem:
The problem is probably the card template where you need to replace {{Reading}} with {{Expression}} on the front side.
(You wrote that you want the Kanji on the back side but I assume that you actually want it on the front side.)
I found the issue. When writing the pronunciation of a kanji, the default cards expect us to put the kanji again in the pronunciation field, and add the hiragana in square brackets, as shown in the picture: