Never had this problem until I installed TP Link XE5300 access points a couple days ago.  All my Kasa switches work fine after the install, and all are remotely accessible - except for one HS200. The other HS200's are still remotely accessible.

While troubleshooting, I removed the switch from the Kasa app and this reset it to factory defaults.  I re-added it and am now faced with the dreaded Remote Control toggle. Like others, the app/device cannot connect to the server.  The firmware is up to date.

My router is an ATT BGW320.  Changing the DNS is not allowed, nor is assgining a device to the DMZ, which I really don't want to do.

It's odd that this happened to a single HS200 when my others were not affected.  Strangely, I can access the switch remotely via the TP Link Deco app, but the scheduling/programming is not the same there.  I really need to be able to manage the switch through the Kasa app when I'm away from home.

If this is going to be an issue with additional Kasa switches/plugs, I may have to start checking out other projects.  I may buy another Kasa switch just to test this out.

Thanks for any help/suggestions.