I run HogPC 3.12.0 (b2351) in Parallels 14.1.3 on a new, updated MacBook Pro 10.14.5 (18F132). Both the MacBook and Parallels [running Win 10, itself fully updated] are fully up-to-date, as is HogPC. 
I can open a live show and make a backup in my HogPC "Shows" folder just fine, so it is not corruption or permissions. But I cannot open an archived (_bck) show file, not even your tutorial show files. And the new backup I just made from a live show is likewise un-openable. I get the same failure drumghys describes in his post "Can't open a backup show (Hog4PC 3.4.0)”  (last updated October 2017). 
I saw no errors in my Parallels Log (or any other log) referencing Hog or its programs. There were no Hog errors in the Windows 10 Event Viewer either. On starting up HPC, opening a regular showfile, and opening the Hog Event Viewer before I log off that show and trying to open a backup file, I see the following:
372341	372342	140	Launcher-1-001c429fa82f	10.0.0.1	Showitems.UnarchiveTask	Debug	launcher-win32-golden.exe	Main	enum Task::Progress::Result __thiscall Showitems::UnarchiveTask::Execute(void)	archive_task.cpp	329	Archive //Mac/Home/Documents/High End Systems/Hog 4 PC/Shows/DF Castle 112017_bck.hog4show extracted in 88ms
372341	372341	139	Launcher-1-001c429fa82f	10.0.0.1	Os.Archive	Error	launcher-win32-golden.exe	Main	bool __thiscall Os::Archive::ExtractCurrent(const class std::basic_string,class std::allocator > &,struct archive_entry *)	osarchive.cpp	142	archive_write_header failed with Can't create '\\?\C:\Mac\Home\Documents\High End Systems\Hog 4 PC\Shows\DF Castle 112017 (2)\~hog3_ident' for archive //Mac/Home/Documents/High End Systems/Hog 4 PC/Shows/DF Castle 112017_bck.hog4show
372253	372253	138	Launcher-1-001c429fa82f	10.0.0.1	Showitems.UnarchiveTask	Debug	launcher-win32-golden.exe	Main	enum Task::Progress::Result __thiscall Showitems::UnarchiveTask::Execute(void)	archive_task.cpp	243	Extracting show from archive DF Castle 112017_bck.hog4show
Seems to me the Launcher app (or the sub-process handling the extraction from the archive - osarchive.cpp? archivetask.cpp?) lacks inherited permission to write the expanded showfile to my disk. That seems like a bug as I don't see a way to increase that subprocess's privileges.
How can I work around this? Is there a 3d party app to unarchive the archived showfile?