@Sequin I am running into the same issue. I bought a bunch of 103 v2 smart plugs a year ago, and now I am unable to configure one (new from same package as other working ones) to switch on/off my Christmas tree. I commented on another thread here about this last Thu, but no response from TP Link yet. 

Meanwhile, try switching your wifi to 2.4G only and WPA2. I heard it helped someone. Didn't help me.

Edit: Fixed it, kind of! So I tried a few older versions of Kasa app for Android. A version from this year's summer did not work either. Version "Kasa Smart 2.17.0.892" from Nov 11 2019 works! It actually has a selection for HS103 specifically. The new app does not have this. The connection and pairing works great. The Kasa app prompted for smart plug FW update, and the plug still works after that. I then uninstalled the old app, installed latest, and the plug is still available and works great after I log into my account. TPlink. Your SW is broken. Please fix it.