Thanks for all your testing. @bigpcjunky 's comment on the Github ticket was really helpful and I'm fairly certain we have it resolved now. Please re-checkout/update fix/neighcrash once more and test.
Some technical details: The underlying heap memory access violation occurred only when there are both, multiple addresses for the same devices in the ARP table, and only some of these addresses are already known to FTL (i.e., they sent DNS queries to the Pi-hole before).
If either all addresses of a device (or likely none) were already known to FTL because they made requests in the past, this bug doesn't show up.
This is likely because users with IPv6 are much more likely to see this bug as there is a high likelihood that an interface has at least one address that has never been used to ask Pi-hole any questions. Multiple addresses on the same interface are rather seldom in the IPv4-world.