It isn't unusual for a Verizon technician to connect both of the POTS line jacks on the ONT to the terminal strip.
Despite both of the sides being connected, L1 is the only active jack.
All tip/ring pairs wiring going to the jacks throughout the house should connect to the terminals on the left side of the strip (the L1 side). If the existing in-house wiring is what is known as JK (aka Jake), the green/red wires may all go to the first floor while the black/yellow go to the second floor.
If the black/yellow wires currently go to the right side of the strip, try moving them to open positions on the left side of the strip and see if that resolves the issue.
