Several addresses are assigned in the contract constructors and assigned to immutable variables. A successful deployment is sensitive to these addresses being assigned correctly for the current network, and that addresses were specified in the correct order. Consider adding checks, as aggressively as possible for the use case, to help ensure the deployment configuration is correct.
.isContract() is referring to the OZ Address library or similar implementation.
This is related to the automated finding [NC-1] Missing checks for address(0) when assigning values to address state variables but suggests a more aggressive check.
