For Halloween/Holidays, we do the “one-shot” anthologies. And for some of my back story… they’re so tightly coupled that I consider them “episodic” and thus, keep it as a single title.
I'd say they should be grouped together if they are related in some way (eg, characters, theme, genre), such that it would make sense to readers why you are posting them as a series of "chapters" and not separately.