It appears that as part of its security routines Apple does do a lot of phoning home. Not to send data but to download things like the latest XProtect signatures database, verify application checksums and signatures to b4r duty sped str legitimate and unmodified, verify subscriptions are current, establish iCloud links and be sure try have the latest data, etc. Because you had/have a WiFi network connection those various tasks each attempt to connect to the internet and eventually time out if a connection cannot be established. Thus making start up and application launch feel glacial. Of course if there is no network connection that can be determined quickly and these phone home tasks are skipped so there is no slowdown. At least that is the explanation I gave myself last week when my internet connection was doing a great job emulating a yo-yo (ie. going up and down 🤯 ) and I was seeing similar inexplicable performance issues. 🤷â€â™‚ï¸
As to the switching between versions, I suspect you may have been re-booting. I have long held the opinion that reboots are not the same as cold boots (shutting down, pause ten seconds, then boot) and can lead to variable, sometimes often undesirable results, so I vastly prefer cold booting. (Installer boots, re-boots are an exception.)
