I have had a similar error after updating to 9.6.1.807, it won't open files it used to open, and presents this error...
Magick.NET-Q16-HDRI-OpenMP-x64: Not a JPEG file: starts with 0x89 0x50 @error/JPEGErrorHandler/614
The file IS a .jpg file, and the former version DID open it without difficulty.