Castle 6.5mm plugs not a tight fit?

I recently purchased a Castle 1717 motor and a Xerun 150A ESC. To connect the motor to the ESC I also ordered a set of original Castle 6.5mm plugs to solder to the Xerun ESC wires.

Now I did the soldering today but now the plugs don't seem to fit/make contact very well. When initially putting the male motor plugs into the female ESC plugs there is some resistance but when the male plug is 'in' I can move the plug back and forth for around 5 mm so there is barely contact between the two plugs (btw, no pun intended here ).

What is going on here? How can I fix this? Maybe use a pair of pliers to bend the female plug for better contact?