Neue Wohnung: Seltsamer Spannungsmangel in den Anschlusskabeln der Glühbirne

Maybe call an electrician? Hard to find the reason without being there

I moved to a new apartment in a new house. I’m trying to connect temporary light bulbs in the rooms. And I had a question, maybe someone knows what the answer to this riddle is. There are three switches for three light bulbs, each switch turns on/off three light bulbs at once. There is voltage in only one of the three sockets! During the move, the movers told me that in order for all three light bulbs to work, “the circuit must be closed” and all three light bulbs must be installed at once. I tried it, but no effect. Everything worked while viewing the apartment, a month ago, the house is new, built in 2022. I’m inclined to believe that I’m not taking something into account/I don’t know, maybe you have any ideas what’s wrong? I don’t want to call an expensive electrician right away… P.S. I tried different light bulbs, different temporary sockets, checked the voltage with a tester (spannungprüfer)