I found a temporary work around, for those on 5.4.4 or other versions that need to use a plugin that hasn’t been updated to 5.5 or 5.5.1 and beyond. Download the nonsource from the epic launcher for that version, it should have the ability to add the fab plugin. add it, and then download the plugin you want. find your engine install location. I went to my nonsource directory/version(5.4)/Engine/marketplace/ and dragged the plugin into the corresponding source engine folder.
This is a temporary fix and I don’t yet know if it will cause issues when upgrading engine version however.