What is the difference between the first export and next exports? Are you changing the settings or something else in the process? Are you exporting the same model?
When you save the project then you will get this error? Are you using just Save or Save as?
Is it possible to upload also this project to the Box (created in 1.3 version)?
It seems like you will need to uninstall RealityCapture using Epic Games Launcher and then install it using the installation file (you will need to copy it somewhere, as it will be removed after uninstalling).
Which account are you using in 1.3 version? Is it the same as the one you are communicating with us?