Raided on PVE

On Phobos found abandoned mine, cleaned it out, replaced core with my own and went out hunting. Was not gone long maybe 30 mins. Returned to see base renamed [RIP] Abandoned Mine, a player named [RIP] Essence leaving the base in what appeared to be his CV and all control of the base was gone from me. I lost all my stuff like 8 cargo boxes. I asked in chat if he took my stuff but got no reply and no admins on.

Just placing a new core to a POI will means it is set to public what means it is accessible for everyone. You had to make sure it is set to your faction or private if I understand you correctly.