Just a guess, but if the HDMI input signals were being provided by cable boxes, perhaps the grounding block that the cable provider should have installed on the outside of the house was improperly installed, or is defective, or is grounded at a point that is too far from where your AC service panel is grounded.
Any of those possibilities could put a huge voltage spike into the HDMI inputs of the TV's in the event of a nearby lightning strike, if they were connected to cable boxes.
Regards,
-- Al
