So, after continue to watch the paint dry on my OS X Finder, I made the following presumption based on my observation that conversion from .cloud files to downloaded target files always complete for each subfolder and I have not observed, at least in the last 8 hours or so, where such conversion failed midway through the list of .cloud files in queue within the subfolder. Assuming the Sync algorithm prioritize completing the task per folder, I thought it could very well be that I may not have stopped an earlier Sync request higher in the directory structure than the parent folder I was referring to and while I may have believed that Sync process may have truncated at each instance of the subfolder completing the conversion, the process may have continued on elsewhere within the directory structure under the ACD. Since I have fair amount of nested folders, it is not easily verifiable. Further, on my OS X Finder, it appears that timestamp of when the subfolder was updated does not percolate up to parent folders; therefore, obscuring any evidence of updates elsewhere. Still, this assumption does not explain why the odrive tray icon's drop-down status indicated that it was ready to sync new changes and not detail any subsequent synchronization occurring elsewhere in the ACD directories.
I decided to test it anyhow and right-clicked on the Amazon Cloud Drive parent directory to invoke Stop. Then I drilled down to the folder I was referring to as the parent folder earlier in the thread (folder containing sub folders of image files) and re-invoked the Sync with Include subfolders & Save and apply to new files and folders checked) again.
Happy to report that it now appears to Sync through the subfolders, at least the last 6 subfolders without stopping.