@David-TP 

Thanks for the input.

First, Fast Roaming is currently disabled.  I could try turning it on to see if that helps, but you are stating to do the exact opposite.  Still worth a try.

Second, Beamforming is enabled.  I would think that would have no impact.

Third, I cannot tell you if the problem happened before with the old router.  We built a house over two years ago and when moving, I set up this new network because I knew the existing one (also a TP-Link product) might not handle the whole house.  That's why I settled on newer technology, specifically a mesh network.  It is pretty good; we live adjacent to a lake and our foster kids report they can connect all the way down there.  That's a testament to the good coverage in the entire house, even surrounding it, with two of these.

As for the TV, it is relatively new (about a year or so old) and at first we didn't notice the problem.  I can't rule out that some new device on the network (e.g., for the time being my Roku) is just causing intermittent issues or not.  All those items you specify do appear non-network related.

I have looked at forcing the TV to connect to a specific Deco (sometimes it connects to the one in the basement which is distancewise further away, but as far as I recall the same issue occurred) and did find a way to do that.  In both cases it's on the 5Ghz band.  I could look to force it if possible to 2.4Ghz, but the Deco doesn't seem to make that easy.

On a side note, I've had issues with foster kids bypassing parental controls because they randomize the MAC address; I have found a way to make that work with static IP address assignments that are explicitly assigned to the device along with capping the range of available IP addresses.  Haven't had any issues since...except for a few disgruntled foster kids... :)  So yea, there could be some magic formula that will solve the issue.  By all means I am not an expert on all this technology, but working in the IT field helps to better understand it, especially when forced to learn something to fix an issue (such as the aforementioned MAC address debacle).

We'll keep plugging away, but if anyone else reading this has any ideas, fire away...