Floating zones keep tripping because nobody grounds the panel lid

Last Thursday I got called out to a doctor's office in Tacoma where the same interior door contact had false alarmed three times in two weeks. The installer before me had the wire run clean, but the panel lid was sitting on a rubber gasket with no bonding strap. Static builds up on that floating metal and every time the HVAC kicked on, it dumped into the zone loop. I replaced the contact first, still tripped. Then I clipped the gasket, added a proper grounding lug to the lid, and tied it to the panel earth bar. Has anyone else run into this where the fix was the cover, not the sensor? I'm curious if other shops skip the bonding strap on plastic cabinets with metal lids too.