I created my own snippets using Credits Left and Credits Right as templates. My Credits Left works just fine but I cannot add My Credits Right to my Timeline. The slideshow I used to create it plays, as does the snippet itself when I right click on it and select Quick Look.
Obviously, I could go back and create the snippet afresh but, before I do that, I am wondering if there are any suggestions for what might be wrong.
Sorry, this is out of my wheelhouse 
I’m assuming when you created both snippets that you gave each a DIFFERENT name than the original ones you used as templates. I don’t think FM accepts one using the same name without displaying the typical “Replace” dialog box, so that gives you a chance to rename it before saving (I’m trying to eliminate some kind of glitch with TWO snippets having the same name, but since they both should be in your MY-SNIPPETS folder, the Mac OS system should take care of duplicates). I’ll try to play around with it, but without knowing EXACTLY what you did, may be hard to troubleshoot.
Hmm?? What bothers me is that there are TWO text layers on each of those snippets, which seem to be duplicated. AND that the text layers don’t even appear on the Start of the slide (now they may be placed OFF the stage area, but when you select those slides the software usually adjusts what appears on the stage so that they show up). I’m wondering why there are two text layers needed, since only one appears during the scrolling.
I dunno – I’m stumped…
Thanks for giving it some thought. It’s strange that the .fms file itself will play when I click on it. Anyway, I was able to use original FM credits snippet and modify it accordingly. Just a bit annoying, since the other one I made works perfectly well when dragged to the timeline.
Might be worth sending the file to Support in case it really is a bug of some kind.