The bug

There is no command feedback anymore when you successfully trigger a trigger. This affects using /trigger without a mode and value (implicit add 1) as well as providing a mode and value.

In 1.12.2 the feedback was:

Trigger [objective_name] changed with add 1
Trigger [objective_name] changed with set 1

How to reproduce

1. Create a trigger scoreboard objective

   /scoreboard objectives add triggerObjective trigger
   

2. Enable the trigger for you

   /scoreboard players enable @p triggerObjective
   

3. Trigger the trigger

   /trigger triggerObjective add 1