Whew, all three of my smart plugs (HS 100 and HS 105 models) are now working correctly with Kasa app, AND with Alexa, But to get to this point, it took removal of the devices and Kasa app from Alexa app, then setting up each smart plug in Kasa again by resetting to defaults and installing anew (with only one plugged in at a time to avoid confusion), and after this was done, re-enable the Kasa app in Alexa app Smart Home section and re-discovering the devices. All worked perfectly again.
This TP-Link Kasa app crash better have been a one-time occurrence at best, or not too often, or Amazon will be exchanging all my smart plugs for Wemo plugs! What a nuisance the Kasa crash turned out to be!