I’m told these engines are not common for head gasket issues but the plastic thermostat housing which is located behind the Aircon pump commonly fractures and leaks .

They can also be difficult to bleed of air correctly. and the fans are designed to autodestruct when the brushes wear out (though yours is apparently OK)

An airlock shouldn’t lead to consistent coolant loss though if its in the process of clearing itself escaping air may cause blow-off from the coolant reservoir. An air lock can thus do a fairly good impersonation of more serious head gasket failure.

I had these symptoms on the Skywing which everybody and his dog assured me was a head gasket failure; which are apparently quite common on these 3-cylinder engines, especially when turbo-boosted.

Cleared itself eventually

These days if I drain the system I clear airlocks by boiling the coolant with the radiator cap off and the fan disabled. I have a large plastic funnel which fits into a smaller plastic funnel which fits in to the radiator fill port, and gives the coolant somewhere to expand.

Its a bit alarming but I think its better than risking local overheating by using the engine normally with an airlock.