Further thought, while the pipes coming into the building are galvanized, there was considerable renovation before we bought the house in the early 1980s with the (not original) English basement probably put in at that time as has/is being done with other houses in this row. The interior pipes are likely to be some sort of plastic. Will have to look under the sink, etc.
The main ground (around here) is required to be on the street side of the meters, because gaskets may interrupt the connection.
A visible cable jumper around the meters is used.
No need for a new clamp, but the connection occasionally corrode.
No need to ““bury a metal plate in the ground) with a grounding wire attached”.
IIRC mine was four or five feet in length, if the earth is soft easly pounded in, the rods are steel and copper plated. NOT REBAR.
Needs a tag: https://www.garvinindustries.com/fittings/grounding-clamps-straps/electrical-connection-warning/j-tag
If the ground is hard, a rotor hammer with a socket is used.
Technically the main ground should be one continuous wire from the main ground (earth) to the main panel.
Hopefully, you have resolved the problem already.