Hi Martin,
wow, you are pretty wrong this time! You seem to regard the connectors as heat sources, while they here actually act as temperature connectors to a heat sink. You could have recognized this due to the fact that the cable is much warmer than each of the connectors. The reason why the cable gets so hot is, because it is thermally isolated by the silicone and the poor thermal conductivity of the air. Meanwhile the connectors are mounted metal to metal to the contacts of the battery and the (electrical) power sink. Both are acting also as thermal heat sinks.
So the coldest of the connectors is actually the best thermal connector. Usually we may expect a poor thermal connector to be also poor electrical one in our situation here, so this would lead us to the opposite conclusion:
The colder the connector, the stronger is the (thermal) connection between the copper of the cable and the metal of the heat sink.
It's funny, how you trust the arbitrary small readings of a multimeter (0.02 vs 0.01) more than math

13.7 Ω/km = 0,0137 Ω/m
How long is the cable that you are testing. Just calculate what its expected resistance should be.
But what you really should do here is to make good use of Ohm's law. You can measure the voltage drops on all of the related items fairly easy. Remember that when you measure Volts, your digital multimeters all have a high impedance. So they do not significantly add to the current in the circuit. Also the test leads of the voltmeters will only have to carry a tiny little current. You could for example add test point behind (seen from the contact side) the connectors by sticking a needle through the cable. As our test currents will be tiny, you don't have to worry too much about their connectivity. It just has to be much smaller than the impedance of the volt meters. You can also remove a little bit more of the insulation and put crocodiles on the wire.
[Contact A = Test Point 1]-<Connector A>-[Test Point 2]------------<cable>-------------[Test Point 3]-<Connector B>-[Contact B = Test Point 4]
With such test points in the cable right after each connector you can directly measure the voltage drop of each part of the circuit.
You may take a look at
the Wikipedia page "Four-terminal sensing"When you do this with a current of let's say 10A, you can get very precise numbers for the small resistor values by an exact measurement of a small voltage.
At 10A you should get 137mV along one meter of your cable. Just adjust it to your actual length and you can verify the spec. As you ability of measuring volts can get much lower, you can even detect much lower resistance values than your ohms meter. Just trust Ohm's law and math

With two extra test points (2 and 3) sticking into the cable, you can measure all necessary voltages along all relevant parts of the circuit:
Voltage between 1 and 2: voltage drop of connector A
Voltage between 2 and 3: voltage drop along the cable
Voltage between 3 and 4: voltage drop of connector B
This would give you much more meaningful results than your temperature values. You may also be able to observe how the resistance values change with temperature.
An other thing that you may want to give a try is to measure the resistance of a connection while you are crimping.
But wait with switching on the load until you have some initial connection. Otherwise you may weld the connection with your current
