This MAC address is already in use (while it's not)

[izykopa]

Hi!
I've got quite surprising for me issue at hand.
There are three assets, let's name it 1 (id=214021), 2 (id=50030) and 3 (id=69607). 
Asset 1 with old MAC was replaced by another device, with MAC address a0:bd:1d:82:16:c0.
When I'm trying to put that MAC to asset 1, I get following info: This MAC address is already in use. (as You can see, it points to asset 2.

Asset 2 has currently no MAC, as setting it up to correct one was impossible too. Because when I try to insert its MAC address (08:ed:ed:5e:f0:3e) it states that This MAC address is already in use. (it points to asset 3).

And Asset 3 is finally the only one that's fine, with MAC 38:AF:29:DC:94:40. Please note that these three MAC addresses are unique, so should not cause any issues. Inserting fictional MAC on any of these works fine too.

Where does the "Already in use" comes from? I trunkated DB, rebuilt the indexes, even shrank the DB via Lansweeper DB tool. Is there a way to clear it without actually deleting and recreating all three assets? I'm almost certain that indeed the hardware of asset 3 was put in place of asset 2, and asset 2 was put in asset's 1 place some time in history during some infra cleanup and maintenance, but wondering why it's impossible to straighten it out in Lansweeper.

I've checked the community and found two other similar topics, but they does not describe exactly same issue, hence the new one. We are talking 11.4.0.4 now, but previous versions had it same (as issue was first noticed at the beggining of this year on V. 11.1.7.1 and 11.1.5.1).