Welcome to MA. we don’t get MINI ones here, wish we did! To bleed my R53 completely I had to open the bleed screw and turn the heater on high then let it warm up till the thermostat opened. Then I would add more antifreeze till it came out the bleed screw. If you did not have the heat on you could still have air in the system. Although you did say the top hose is getting hot, that sounds like it is circulating coolant.
You say coolant is bubbling in the expansion tank, this could be a sign that you are getting combustion gas in your cooling system. Did you have your head checked to make sure it was flat before changing the gasket?
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