I would recommend following the guide below before following this guide.

https://defusestudios.com/sgk-fixed-no-owner-warnings/

Go to the BP_PlayerInventoryComponent then select and change all the variables shown in the images below to RepNotify for the Replication setting. If you have any of your own equipment slots added you will need to do the same to that variable as well.

Next create a new function in the BP_PlayerInventoryComponent called Update Equipment Component and add a new input called Equipment Slot then set the variable type to S_EquipmentSlot then copy the image below.

Next using the OnRep_ functions created by the equipment variables copy the images below. If you have your own equipment slots you will need to do the same for that as well.

Then select and change the variables shown in the images below to RepNotify for the Replication setting. Both variables are in the BP_PlayerInventoryComponent.

Next in the OnRep_HeldActor function copy the image below.

Next delete the highlighted node shown in the image below, location at the top of the screenshot.

Next add the node shown below, location at the top of the screenshot.

Next go to the BP_MasterHoldable and select the class defaults and search in the details for “always” then tick Always Relevant like the image below shows.

Next select the custom event shown in the image below and set the replicates to Run On Owning Client like the image below.

Then add the highlighted nodes shown below, locations at the tops of the screenshots.

Next you will need to replace the nodes you have in the locations shown in the images below with the highlighted nodes shown in the images below. Locations at the tops of the screenshots.

Next go to the FirstPerson_Anim blueprint and add the highlighted node shown in the image below.

Then go to the ThirdPerson_Anim and add the highlighted nodes shown below in the images, location is at the top of the screenshots below.

Next go to the BP_MasterMeleeWeapon and add the highlighted nodes shown in the images below, locations at the top of the screenshots.