Hello, I just dealt with a similar problem. For no reason at all, my vault was showing as completely empty in the Epic Games Launcher. Here’s how I fixed it.
Sign out of EGL.
Sign back into EGL.
No assets will be in the vault at this point, and I don’t even know if this is a needed step.
Go to your vault on the Unreal Marketplace (in a browser.) and select an asset which you own, and try to open it in the EGL.
Doing this caused my entire vault (over 600 assets) to load back in. Hope this help!