Airfoilmod:
I think the purpose of the Fuel/Oil Heat exchanger is to cool the engine oil with fuel on its way to the combustors.
Correct.
The spanner is the melting of water ice built up in the passages of the unit which then is injected and possibly quenches/prevents combustion.
Wouldn't lead to cavitation. Perhaps the spanner is a mix: release of ice build-up in and/or before FOHE causes obstruction.
The unit can be cooler than is planned for when long periods of exposure to high altitude temps and little power demand keep the oil cool and allows for ice build up in the HE.
Quite likely. And its position vs that of other powerplant mfg's.
What hasn't been addressed adequately imho is the presence of water in the fuel.
As in the tested samples from BA038, or fuel in general?