This is a fairly recent problem since we last updated enscape in December. To start I noticed that our whole custom asset library was blank after updating even though it was pather to the same location as before. So I tried re-pathing and same issue, I checked the folder to maker sure the files still exist, and they were still in the folder. I then went to another team members computer to check and they were experiencing the same issue.
After some hasty back-dates to previous folder versions I was on the verge of giving up because nothing has been added to this folder in almost a year and it all worked fine before the latest update. I even tried uninstalling an re-installing enscape and no avail they would show up. I then decided to repath the folder one folder structure back, as in if the previous folder was located in Desktop -> Enscape -> Enscape Assets -> Custom Assets I am instead pathing it to Desktop -> Enscape -> Enscape Assets. And boom this solved the issue of not being able to see or load my custom assets.
Now onto the side affects of this change, I now have unbearable load times when I click my custom asset folder, these were not there last time the library was working. Now in your defense I have about 164 custom models and they mostly consist of 3D Render People and High Poly Trees. Though this load time was not present before, not sure if this is user error, a bug, or a product of my own creation.