The MAC starting with a OUI of 8A:86:CA is a locally administered MAC (as its U/L bit is set correspondingly), and therefore wouldn't be registered in any offcial OUI database.
This would suggest a MAC created either by applying MAC address randomisation or generated by some kind of virtualisation software.
The latter is less likely, since many VM providers have registered a OUI despite the fact that they assign MAC addresses locally (e.g. 00:50:56 is a VMware MAC).
The former may be applied by some smartphone OS for connections to potentially unsafe wifi networks. Usually, this behaviour is configurable.
Do you use smartphones and/or VM software in your network?