How to meet the issue:

1. Go into a world, and make sure the world has entities besides you.
2. /tellraw @s {"selector":"@s"}

   , and you see your name. When you hover on or click your name, you see nothing.

3. Select not only one entity, for example, /tellraw @s {"selector":"@e[limit=2,sort=nearest]". You see your name and another mobs name. Hover on either of the names, you see its type and uuid. When you click the name of the player, you see "/tellraw ..." normally.

Doesn't only affect the hover effect, all components except plain text seems to be affected. See comments for more info.