I use it on iPad Air and Smart Keyboard.
The environment is iPad OS 15.0.2 Textastic 9.7.2.
When I move the cursor with the cursor keys or tap the screen while inputting Japanese, the cursor sometimes disappears.
I don't know the location of the cursor, and the location of the cursor doesn't change in the first place.
It has happened in recent versions.
In addition, we have confirmed the occurrence on iOS 15.0.1.
Customer support service by UserEcho