It's probably fine, if you put it in a separate section, clearing indicating that you are guessing.

At work we have an optional "diagnostic" section in our ticket template, mainly intended for the team, but I'd be happy to see a user try to fill it. At worse it's harmless, at best it gives the actual reason, somewhere in the middle it can give ideas even if it is wrong.

I wish. It happens very often that such speculation derails the whole investigation. It really shouldn’t, but people are people. If the title of the bug report says that the foobar is broken it might take weeks until someone realises that they were wrong and actually the problem is in the frobnicator which feeds the foobar.

Especially when because of this we assing the investigation to the wrong team. The foobar people don’t want to appear as if they don’t take the bug seriously, but all they check everything looks normal on their side.