Hey @Anonymous .
Offline devices will typically drop off after 30 days of no connection but there is no way to currently delete them manually. If you have MAC randomization enabled on devices, each time that device changes its MAC address it will add the same device as offline again since the devices are identified by the MAC. The same is the case if you change the name since you changed a property of the device.
In short, any information that can be received from the device that is changed on either end after an initial connection is made can cause an "offline" entry. There are other scenarios too that can produce an entry but this is the most common.
