Failed to Find/Load Assets Error

Hi, I keep having a “Failed to Load” error when starting up my project after importing an fbx file, saving and closing the project. I use the “Import Into Level” option from “File” to bring the fbx file into the level, it loads fine and I can move and edit it without problems. I make sure to save any changes to the project before closing it, but when I open the project again I’m greeted with a “Can’t find file for asset” and “Failed to Load” messages, and all the static mesh actors associated with the file are gone.
This doesn’t happen when I use the “Import” option from the Content Browser, but this only allows me to apply texture to the 3D model as a whole rather than to individual components (unless there is a way around that?), which is something I need to be able to do.
Can anyone help? I can’t make any progress in my project because all the adjustments I make are effectively gone when I close the program. I’m very new to using Unreal Engine 4 so I don’t know if I’m doing something wrong or if it’s a possible bug in the system. I updated to version 4.12.5 and this issue still persists.