Are your doors locked? Are you building out of stone or above structure tiers? Do you have base defenses like turrets or species X plants? Are you using vaults to store your valuables? Does your base have multiple levels of structural defense (like 2+ walls)?

Your post wasn't very descriptive on how the suspect is getting into your base. We do have rules about repetitive raiding (harassment), but if you leave your valuables in the open for anyone to take it's hard to police that. The server is PvPvE which means PvP is in there, so you also have to take those extra precautions to ensure your safety and the safety of your dinos/items. Do you know the name of the person doing this? Tribe log evidence? Etc?