First there are some Is Valid nodes that need to be added to some widgets. So start by add the highlighted nodes shown in the images below, locations at the tops of the screenshots.

Remove highlighted nodes shown in the image below, location at the top of the screenshot.

Next in the BP_PlayerInventoryComponent create a new variable called Bool and name it Level Load, then copy the image below. Location at the top of the screenshot.

Next save and close your project and download and unzip the folder linked below. Then copy the content folder that you just unzipped. Now go to your project folder it should look similar to the image below.

https://www.dropbox.com/s/dnf9r2gyzdscbrx/Content.zip?dl=0

Now paste the content folder you copied in to this folder, you should get a warning, click Replace the file in the destination. Once you have done this you are done. If you want to know about the new save system feature check out the Feature Guide linked below.

https://defusestudios.com/save-system-rework-feature-guide/