Here’s to hoping this is just a failed pressure sender, but failing on both circuits simultaneously seems a bit unlikely, unless they share a single Gnd connection.
Pressure relief valve sticking at start does appear to be a fairly regulator occurrence.
Oil pressure then noted at between 0 and 5 Psi.
Does this sound like an Oil Pressure Release Valve issue to you? - E-Type - Jag-lovers Forums
Oil Pressure relief valve stuck open - Saloons - Jag-lovers Forums
Oil Pressure Relief Valve Help - E-Type - Jag-lovers Forums
If the relief valve is sticking open, it begs the question why is the oil pressure above 80Psi, especially at cold start…unless the driver is revving the engine to high revs, which seems very unlikely.