@ ChristheCo Thx for replying. I found below two topics reporting the same bug, for you to track.
Trebuchet projectiles don’t have an impact animation after chemistry has been researched - Age of Empires II: DE / II - Report a Bug - Age of Empires Forum
Still no hitting particles of trebuchet with Chemistry researhed - Age of Empires II: DE / II - Report a Bug - Age of Empires Forum