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I have had this happen too. Does your Orthographic Viewports show no grids? If so, this could mean that your camera is set to close.
Open the Camera Attributes from one of the Viewport Windows. The third smallest camera icon from the left-side will open the Viewport's Camera Attributes or click on the Viewport's "View" Menu and select "Camera Attribute Editor". Under the Attribute Editor > the "Camera Attributes" appear. Under the section called "Camera Attributes" > increase the number value for the "Far Clip Plane" by a lot (i.e. shows 10,000 bump it up to 1,000,000, if you know that your object is large). Then you should see something in that single Orthographic Viewport. Now, use shortcut key "F" to frame the object in the Viewport Window. If the entire object now appears you can just repeat this process for the other Viewport Windows.
If this doesn't work, then check to see if your Channel Editor is showing extremely ridiculous high number values. If that is the case, then that might also be a reason as to why the camera's Far Clip Plane needed adjusting.
I have had very good luck with this process, so I hope it works for you as well. Good luck!