I submitted my original support query over a year ago and received no responses. Essentially, I gave up on using the product because of the issues. In the interim, did some minimal investigation of this problem. Here is what I found:
(1) My “jpeg” images are all tagged using the EXIF and IPTC tag sets.
(2) It appears that F-Stop acquires most of its metadata from the XMP tag set. Although, it seems that the GPS location information may also be acquired from the EXIF tag values.
(3) I noted that those images where F-Stop reported tag values were all values which had values in the XMP tags in addition to the same values in the EXIF and IPTC tag sets. For those images lacking values in the XMP tag sets no tag values were reported in F-Stop.
(4) The obvious solution in my case would have been to implement a mechanism to propagate EXIF and IPTC tag set information to the XMP tag set. To date, I have been unwilling to undertake that effort.
Hope this make some sense and explains what was initially a confusing situation.