Click-event in Chat is positioned one line to low. If you click on the word in chat that is suposed to trigger the click event, nothing happens. You have to aim one line lower to trigger the event.

How to recreate:

1. Create scoreboard

/scoreboard objectives add SLSZS trigger

2. Enable trigger for player

/scoreboard players enable @p SLSZS

3. Execute this command with a commandblock:

tellraw @p[]
[

{"text":"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" }

,

{"text":"\nStation auswählen (im Chat anklicken):" }

,

{"text":"\n[Dornwalden]: ", "color":"red" }

,

{"text":"Hauptbahnhof, ",
"clickEvent":

{"action":"run_command", "value":"/trigger SLSZS set 50000000" }

,
"color":"red"
},

{"text":"\n[Gelbe Linie]: ", "color":"yellow" }

,

{"text":"Venezien, ",
"clickEvent":

{"action":"run_command", "value":"/trigger SLSZS set 30800000" }

,
"color":"yellow"
},

{"text":"\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" }

]

If you now try to click "Hauptbahnhof" in chat, nothing happens. If you click one line lower on "Venezien", you recieve the message that the scoreboardvalue is set to 50000000. This should have happenend when you clicked on "Hauptbahnhof".