When soldering XT connectors for RC motors, advice is to clip the 2 halves of the housing together first so even if the plastic housing gets hot/soft, the pins stay in the right position.
Spending time soldering connectors then finding the melted bits won't fit together is something you only do once. That's what I got told. Never again.
Got the 50A Anderson connectors fitted. Went together OK. Ended up using plumbing solder and flux to fill up the connectors held vertical, then dipped the wires in. Used a small gas torch. Pretty much as per @ukracer 's link above.
The printer is back and running with no sign of overheating at these terminals. Pointed an IR thermometer at it and all good.