Is the tank meant to be a hover tank? How is the tank mesh setup within the BP, how are the controls setup? Can you post a screenshot or a quick video showing your setup? With out seeing exactly how it is setup I can’t really point you in a definitive direction I can only point you in a few.
Direction 1: check your BP’s default use of the controller rotation axis.
Direction 2: If you are using a spring arm for your camera do the same thing, disabling or enabling the use controller rotation axis according to your specific needs.
Direction 3: Make a copy of your BP and try using the tank mesh as the BP’s root component so that all other sub components follow its rotation as a parent.