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?

@tye hello, you may need to provide a little
More information.
What is the trip level of the RCD supplying the system?
What happens if you disconnect the load on the output of the multiplusses?
Do the multiplusses ever sync to mains or are they constantly in inverter mode?
Why is the input level set to 6 amps? Is that 3 amps per
Multiplus? Does that make sense given you have 10kVA of inverter capacity?
What is the system used for? Is it ESS, Marine, off grid?