Boris Sentry Gun explodes instantly very often

@CountSero Same thing happened to me. I only play Breakthrough. It just exploded randomly no matter where I put it, on the ground, on boxes, containers, etc. I can't find a pattern to how it's happening.
I'm mostly play Boris and trying to max my sentry mastery. But it's already hard as it is, and when it exploded after a few seconds after being placed, it feels impossible to achieve.