This is a workaround for the problem that the last character of the conversion candidate does not disappear and continues to be displayed at the cursor position when converting to Japanese with GNOME, the window manager of Linux.
No matter how much I search, it doesn't appear, so it may only occur in a special environment, but I wrote this article for people who are experiencing the same symptoms and for myself in the future.
It occurred when I put Gnome in Ubuntu of local installation and input Japanese using ibus-mozc ("Google Japanese Input") that was included as standard.
Ubuntu 18.04.4 LTS GNOME 3.28.2 ibus 1.5.17-3ubuntu5.2 ibus-mozc 2.20.2673.102+dfsg-2ubuntu0.18.04.1
When trying to convert to Japanese on the terminal etc., for example, if you enter "Japanese", think again and delete all the characters in the backspace, for some reason only the last "go" does not disappear and remains displayed at the cursor position I will end up.
Change IME to Anthy, which was mainstream before mozc appeared. (I've been using Canna for a long time)
Installation of Anthy
sudo apt install ibus-anthy
Change IME Select and change the menu in the following order
Settings-> Region and language-> Input source "+"-> Japanese-> Japanese(Anthy)
In my environment, the above solved