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Even the schematic diagram is not too clear, but i will try to explain what could be happen.
As the RCBO tripped, and we know that all RCBO have ” Thermal & Magnetic protections + Earth Leakage protection ” there's 2 possibilities :
1 – The tripping order was from ” Thermal or Magnetic protection ” and in this case we had either an over-load or short circuit, where we can know which of them as follow : if you tried to close it without success for a few minutes in this case the tripping's order was from Thermal protection, or it closed but immediately re-tripped in this case the tripping's order was from Magnetic protection.
2 – The tripping order was from Earth Leakage protection, and in this case we have 3 possibilities :
A – There's a leakage current, either permanent or transient, more than ” IΔn “, if permanent you can't re-close the RCBO, but if transient you can re-close it again.
B – We know all the all kind of PC have a transiant leakage current and a big value of Crest factor that cause some distortion of the current, for these reasons we use for this kind of application a special RCBO or RCCB that have ” High Immunity “.
C – At the moment of supplying a PC the inrush current is, in some case, bigger than the Magnetic protection, so, the RCBO will re-trip immediately. for this reason it will be better to use ” C curve ” or in some case ” D curve “.
To be able to clarify more, it will be better to have the Single Line Diagram, because as you mentioned that there's 800A MCCB, then 100A MCCB and 100A I Switch, then 63A MCB and 63A Switch, then the RCBO or RCCB.