Check the cable between the PLM and the ISY, make sure the ISY ports did not get swapped.
Cell phone chargers, flat screen TVs, CFLs, florescent ballasts, UPS/PC power supplies can attenuate Insteon signals (FilterLinc is solution) are some items users have reported as causing problems. Verify the 120V legs are still coupled. Wiring changes could have put Access Points on the same 120V leg. The easiest way to isolate appliances causing noise is to unplug them. Turning them Off is not enough as the power supply is usually still connected energized.