When using the /tellraw command, the tag names have to be delineated with double quotes, otherwise the command will not work.
Example:
When issuing the command
/tellraw @a

The input that comes out says
Invalid json: malformed JSON at line 1 column 3
However when you write the command as
/tellraw @a

the command works with no issues.
<Fog> Hehehe...

This wasn't necessary to do in earlier versions. Now it is, and it is time consuming.