Southwest's wifi is likely sending 'deauth' packets to devices with poor link speeds. The reason for implementing is that one weaker connection can consume a huge portion of the wifi control channel which has fixed limitatiins.

I fly 8x a month and first started seeing this happen late last month.

To help improve connections see if your device has the option to force 5ghz-only radio (instead of the more congested 2.4ghz). Also if there is a WiFi power saving option turn it OFF