I have been having this issue for a while now and never knew why the direct link will just randomly brake. Assumed it was still some bug that have to be looked at and fixed. I have found a work around by rather exporting Revit to FBX and importing the FBX file into TM.
Unfortunately when trying reload a new Exported FBX model with changes I had to make to the project in Revit into TM. The Import went all wired with random objects missing and other completely out of place.
I decided to try a new direct link to hopefully get the the project to import correctly which worked. So while working with the direct-link I forgot about a few changes I had to make to the Revit project. I took a chance and tried to sync the direct link and to my surprise it worked with no issues. At the same time I realized that I have not yet Saved and synchronized my Revit file to the central model. I made a few more changes to my Revit model and tried to synchronize using the direct link.
This was when I released the the direct link gets broken as soon as you synchronize your Revit model to the central Revit model. The error is as as per picture attached.
Epic games please can you look into this as practically all our Projects works with an central Revit model and renders the direct link useless and unusable with a central Revit model.