Several Models Stopped Working

Several of my models -- previously working with no problems -- have suddenly stopped working. Repeated attempts to generate images using certain models in my list now result in nothing but spinning buffer circles and "time out" messages. NO GENERATED IMAGES. It's tempting to reupload & retrain new versions of the same models but what's to say this problem won't crop up again? PS - In the meantime, other models in my list continue to create excellent results. What gives with the seemingly random model failures?