It's either that the settings are not exactly identical, or you found a regression. It may be some specific scan that is taking time, so I would recommend turning scanning options off one by one until you determine which one is culprit. We can then look into it.
If the Display inactive devices is unchecked, but inactive devices are still shown, it is usually because Allow ARP outside current subnet is checked and the router responds to every ARP request with its own MAC address. In this case you will see that all devices have the same MAC address. Simply uncheck this option and the software will only send ARP requests within the current subnet.
If these issues persist, please submit a support ticket and send us the relevant screenshots and your XML config file.