@td47 Thanks again for your recommendations and you're welcome on the feedback.
Just to update here. I am still having success in opening the apps if Sling TV is the first thing that opens after this TV powers on. This has been consistent since you recommended the "channel" fixes on @Clipped's router.
There was a Sling TV update after that - which I accepted - but it doesn't seem to have affected anything one way or another. I'm not sure if that's the app causing this either, as most of my factory resets failed to launch apps after it worked only during the first one.
I suspect the router situation might have something to do with this, although this doesn't explain why my prior LG "UM" TV is still working fine from 40 feet away or so (I also haven't accepted a recent update for it yet, in fear that it might itself in a similar situation as the "UN" TV in my living room). The apps situation and structure is pretty much the same between the two as well.
I have considered upgrading the router and modem to a more current one in hopes it might jump start something. But I hesitated when my mobile hotspot connection and a ethernet one from the router didn't make much of a difference, if at all. But if this continues, I might check out replacing them with a 2-in-1.
@Clipped Yeah, this is a user-based forum, I believe. But I did call LG's warranty/help line to get some additional ideas on how to fix the TV (as I'd registered my TV with them right away). When those weren't successful, they sent me to a different tier on the same line, to launch a complaint so that they could send a technician to my place to take a look. I've only had this TV since June 30th, so it's within the year-long manufacturer's warranty. However, the technician hasn't called me to set up a time yet in nearly 2-3 weeks. I did call LG again to let them know that, and they'd say they prioritize this. But I still haven't heard anything back. It's not a big deal at the moment since I'm able to open the apps on the TV again (although in a more limited way), but their number is 866-558-2559, in case you want to look into that.