Hey StreamerUser thx for echoing Dan's advice that a hard reset wouldn't delete the YTTV app. All makes sense.
Re 'older/lower memory models'... Likewise makes good sense. My Express+ being one of the lowest capacity device models probably has a lot to do with this hiccup. Also, it came from Walmart whose local stock may not turn over often, so it's possible my hardware is an earlier version of the model. Maybe not classically obsolete yet still might be prone to get tripped up as evolutionary updates to certain more complex screensavers roll out to Roku devices over time.
Also good catch re the slight difference in version numbers! I reviewed the pics I took with my phone and yep I now see that I totally missed that leading digit. Thanks for explaining that there are indeed two Aquatic Life screensavers.
As for v13.~~~ (the version that cannot be removed from My Screensavers)... It sounds like this one basically now stays in My Screensavers and on purpose. So, is this some sort of a Roku-suggested choice that's intended to be seen, or what? It's not bothering me having a screensaver I likely won't use again occupy space in 'my' list per se. Just mildly curious as to why an end-user has no easy option to manually remove something from his/her custom listing -- if nothing else but to reduce unnecessary clutter.