Glad that appears to have fixed the mysterious failure!
These days, especially with Laza's JSON-driven skins, processing only one subdirectory (i.e., the one to which you just added a few images) can leave you with a broken album. So, changing that setting has become the "go to" first shot at fixing things.
Even in a non-JSON skin, like one of mine, I don't leave it set to process only updated subdirectories unless I'm
very sure that I haven't updated the jAlbum core or the skin since the last time I built the album, and that all I'm doing is adding a few things (the family website photo album being the prime example of that).