A relay would be more reliable than this design.
Mosfets have PTC so RdsOn increases 3x when hot.
These devices are obsolete, you may consider some that are 10 mOhm like SiC types or GaN in one device.
You dont show any debounce circuit or wire inductance and resonance is likely during switch off causing SOA issues with high gate R.
- make Rg ~ 100x RdsOn of diode is used for turn off fast .
-there is no Zener OVP transient protection builtin this device.
Slow Switch energy limit should be <<300mJ or 0.3VA-second . Or 363mJ abs max...
Power sharing 3000W in 20 FETs only works all device thresholds are perfectly matched so during switching off they share lagged inductive current.
normally it is switched off fast with a diode.. Not turned on fast as your design attempts and then turns off slow with 1500pF Ciss per device.
Repetitive Switch Energy limit is only 4.5mJ and without Zener or MOV and if switch bounce, You can expect failures.
3000W if switched off in 1us is 3mJ ,
Consider if all FETs on one heatsink and all pins ganged 20x1500pF=30nF would might need Rg of 30 Ohms to switch <1us.
Since these devices are avalanche mode, it is impossible to guarantee thy all switch simultaneously with variances in Rg Ciss product. But perhaps you were trying to slow down the avalanche time to current share during off with a slower response time. Not easy with wide separation of wired devices.
Consider a Relay or a better 3kW switch from Cree, Diodes inc in the 1 ~10 milliohm range in SiC type.