Hi @K_Hege90 ,
What type of account are you using? Is it an IMAP or Exchange account?
Do you have sync and access your mailbox and/or calendar on multiple mobile devices? If so, you should start with disabling all the syncs that have been set up, create a new meeting item and see if the issue continues.
If you are running antivirus software, it is recommended that you turn it off temporarily, and if you do not create duplicates after sending the invitation, you will need to uninstall or close it while sending the invitation.
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