When you upload IFC files to the model server and e.g. synchronize the IFCSpace's with rooms in dRofus, there will be created strings between the IFC and the tables within dRofus. This may cause problems when you try to replace single IFC files within a model on the Model server.
As a general rule we advise to delete the entire model (not just the single IFC file) when you want to replace IFC files. You can do this from the red cross icon in the top left corner of the Model connection interface:
Then create a new model and upload your IFC files.