What you were expecting to happen, and what actually happened:
Mechataur spell says splash damage but side bubble description and actual spell does LIGHT splash.
How often does this happen? When did it begin happening?
All the time. Light splash damage issue at least 1 month ago. I don’t remember this issue at Christmas.
As a follow on - the spell says it could silence enemies affected. The splash damage can’t hit an enemy if there is a space and then the next enemy is after the space, but they did get silenced. Here is an example where green arrow is damage and white arrow is silence.
No worries, bugs in this game often have to be reported over and over again for anything to happen. The first bug report was in January 2021, so more than 2 years ago.