I now have straight 6 days of KP115 operation without them vanishing from Sense. The plugs have been solid since the minute the firmware* in my Deco routers was updated (TP-Link Deco M9 Plus mesh routers). TP-Link support gave me beta firmware to fix a separate issue: one of two HS300 power strips would not ‘add’ in the Deco app.
At the moment, I have 2 HS300 power strips, one is behind the TV less than 3 feet from the router, the other is in the garage 25 ft away. I have 3 KP115 plugs, one behind the refrigerator (~15 feet from the router), two are in the garage (35 and 45 feet and several walls away). All five of these monitoring devices are showing now in Sense for the last 6 days (the HS300s never had any issue).
Off track, but I counted wifi devices in my garage and found that I have 16 there: 2 wall switches, the Sense, Rainbird lawn irrigation system, HS300 6 plug power strip, HS105 plug, HS107 dual plugs, 2 x KP115 plugs, MyQ garage door opener. The KP115s were the only devices to have issue with Sense, and none have trouble with wifi connections or the Kasa, MyQ or Rainbird apps.
*The issue with the HS300 not adding in the Deco app was due to the firmware having a limit to the number of plugs (32) they could accept. The Kasa app had no such limit and allowed all the plugs and power strips to be added and configured.