Some versions of Photoshop have a bug where they sometimes save garbage into the full-size preview image. There's no reliable way to detect that the preview image is garbage, that we know of, so we just display what is in the file. The issue is on the Photoshop side rather than our side, and the problem is baked into the files which exhibit it. Re-saving them in a newer version of Photoshop may fix them.
You can configure Opus to always use the smaller thumbnail image, including in the viewer pane, but it will often be quite small:
