The first thing you do in this case is to confirm if you can see the model at all. For example, if you click on the IFC file tree in order to highlight it, and then you use the viewing cube, will the model appear (even briefly?):
If your model seems to appear only to disappear right after, or if it generally behaves in a glitchy manner, this might very well be caused by how your coordinates were set up.
Just like with Revit, our Viewer cannot process large coordinates,. For example: if in your original model, the distance between the survey point and project base point exceeds a few KMs, our Viewer will then process the scale of the model based on that distance. This large scale will cause the model be tiny and disappear as soon as you attempt to manipulate it. Sometimes, using 'world coordinates' can cause this as well since they're larger.
Make sure you've established the 'shared coordinates' between your models. More info here: https://help.bimtrack.co/hc/en-ca/articles/360041885511-Setting-Up-Revit-Shared-Coordinates
If the issue is different that what is described or after setting up coordinates still not working as expected, you can reach out to support with screenshots and details about your project setup. Including were was the model created and how it's behaving in a glitchy manner.