I am not getting what is suspicious exactly. Anyone could wake up and change account credentials. That doesn't mean they are doing suspicious. As long as they aren't abusing the forum you can't take action against anyone unless there is transparent evidence of changing hands. By the way, I am pretty sure you are posting from your alts.
I do not have any doubt that the OP is using his/her alt account to create this post. And I have not got any suspicious activity that can prove the ownership has been changed.
-The account changed email and password simultaneously.
Then, what does that mean?
The password has been changed two times recently but there is still no evidence that the hand has been changed. If hands are changed then the account can be sold and that can be used for scams.