Mailbox Delegation keeps being added

[SonnyFisgard]

Looking for some help. We're working with a hybrid 2013 & O365 Exchange environment. I keep having Mailbox delegation being added to user accounts that we are not manually adding. I keep removing the delegation but it keeps coming back hours later. 

Wondering if this is a know issue, or if there's someone that might have seen this before.

Thanks

[#2]

Check the admin audit log.

[#3]

Try checking automapping via powershell, get-aduser "username" -properties msExchDelegateListLink | Select msExchDelegateListLink