So, the messages in the Logs mean:
FOUND WeMo AirPurifier --> A device with type “Belkin:device:AirPurifier” was discovered on your Network and the “PARSED” line shows the MAC address that you can match with your Air Purifier; So, it’s finding your Air Purifiers and with different MAC addresses (from the logs);
Device was already found in state --> When the Device is created in SmartThings it uses the MAC address for the DNI (Device Network ID) and this message means that a Device with this DNI (MAC address) was already found/created in the Device list. Looks like you already have both Air Purifiers (their MAC address) in SmartThings for some reason.
And that’s why I’ve assumed you had already installed the SmartApp “WeMo AirPurifier (Connect)” .
But since you said that you don’t have the SmartApp you’ll have to look your Device List (IDE -> Device List), ordered by “Device Network ID” and try to find the Devices using the MAC address.
If you find them, you’ll have to remove them. manually or using the other SmartApp that created them to be able to reinstall them.
Good luck again