The disappearing assets issue you're experiencing may be caused by assets overwriting each other. A device will be overwritten by another device if it shares one or more MAC addresses with the other device. Shared MAC addresses explain the behavior you are seeing. You can blacklist the shared MAC addresses to prevent an overwrite, but keep in mind that each device would still need to have at least one unique MAC address.
If you would like to attempt blacklisting MAC addresses, a sample script for doing so can be seen below. You will need to insert the shared MAC address into the script and run it under Configuration\Database Scripts. Proceed with caution when running scripts and always create a database backup first. Backup instructions can be found in
this article. If you're having trouble finding the asset other assets are being merged into, the asset that received merges will have an entry in the comments tab indicating a merge happened.
INSERT INTO tsysMacBlacklist (Mac, Comment) VALUES ('00:00:00:00:00:00', 'your blacklist comment')
GO
UPDATE tsysupdate SET MacBlacklist = GETDATE()