A small piece of dirt, in other words something that has no effect in an electrocic circuit. But 5 megaohm is even less noticeable. One would expect a level 100 to several 1000 ohms for an effective snubber in the present case, resistor power ratings should be respectively. A snubber can be helpful, if the circuit wiring is bad and can't be easily improved.
I see. Without knowing the actual device wiring, I won't dare substantial statements about circuit operation anyway.
People would use a low impedance gate driver, e.g. an industry standard driver IC like TC42x and gate resistors in a 10 ohms order of magnitude.
With reasonable circuit wiring, there won't be a spike problem.
I don't even know which 80N60 type you are exactly using. There are different ones. But I won't expect that unequal current share is the primary problem.
By the way, operation mode hasn't be told at all? Switching frequency, duty cycle?