Loss of annotation in pdf files despite autosave

Using Adobe Acrobat reader. My PC closed down unexpectedly from sleep mode with 2 pdf files open. Both were set to autosave every 5 minutes and filed in OneDrive. On reopening, all my annotated comments had been lost and I was back to the original file. I am unable to find where temp files are stored, nor see any means to recover the annotated files.