2 x Multiplus II 5000/48 parallel tripping shore power

We have two inverters in parallel that will not connect to shore power.

Input limit set to 6amps. Both inverters connected on AC IN.

Shore power is through standard RCBO protected circuit.

When shower power is turned on inverters switches make loud clicking noises and after approx 15 seconds trip the RCBO.

Any idea what configuration changes can be made?