Switch now activates two sets of lights

I had an old Edison fuse box replaced with a breaker panel this week. Tenant called to tell me the lights weren’t working. When i went to check it, here is what i found. So i have two sets of 3 way switches, one turns on can lights in the front room, the other set, a light in a hallway. I checked the wires, all were connected. Checked the lights. And they all had power to them. Switched out bulbs, still didn’t work. Couldn’t figure out what was happening. So i hit the switches again. And found, that one switch now turns on both the can lights, and the hallway light. But only all 4 switches are manipulated a certain way.
I never had any issue before i replaced the fuse box.... so it has to be something there. Any ideas??? I am at a loss.