In most cases, logging out to the character select screen again and then back in or loading into a brand new zone will resolve group-related issues.
If the issue persists after re-logging, you can try reforming the group you were in when the issue occurred and then disbanding it. You can also try joining a large group and asking the group leader to disband it. This can help reset your UI. To prevent this from happening in the future, we recommend not logging out of the game while still in a group.