So, several people share the router and can modify settings...
That's a recipe for trouble.
I do external support for small businesses. When I work, configure etc. sometning, I change the password. I write the password on a piece of paper and put it in an envelope. Then I sign across the sealed flap. That envelope is handed to the customer. If I cease to work for them or something happens to me, they can open it and retrive the password. If something goes belly up, I ask for the envelope. If the envelope has been tampered, I wash my hands, and chrge handsomly to solve the issue.
I'd reset it, and then make someone responsible for doing things to the router, that way everyone knows what's going on.