Any type of interaction with the editor like using a mention, inserts the mention yet send you away from the line you are one. You can usually place the cursor at the end of a line of pure text without the jump. But try to place the cursor on an empty line and you jump.

Sadly I have to never switch my worlds or article from the Legacy editor because they can not be switched back. In the article list there is even the choice for the Old WYSIWYG editor (which caused no end of grief) yet the legacy editor which caused no problems and functions fantastic on mobile is no longer a choice.