It used to be all done in foreground on console boot with the boot not finishing until they all done, but I think they changed it to make the basic pfsense system come online quicker so now it does some of it in the background after the UI etc. is loaded. Then at that point have to hope it works out ok, I think its the same process as used when doing a in place upgrade which also reinstalls all packages.
I am guessing they did this as was people doing these in place upgrade's without console access and getting impatient waiting for the UI to come back up.
I discovered one reason package installation is kinda iffy on my configuration.
I got a backup router and was copying my configuration over while using only 5G (as I can plug two devices into that without disrupting the main router) but because AAISP L2TP is part of my configuration it kept trying to connect which obviously clashed with the existing connection from my main router.
So the firewall kept restarting each time the L2TP connection was rejected, causing package installation to abort. I disabled L2TP and manually installed the packages.
Now I hit a second snag, the N100 seems to have a transient current peak during bootup that overloads my PoE splitter.
I honestly didn't think this unit would peak over 30W (though some Amazon reviews did say my PoE splitter had problems hitting its rated output) and 60W PoE++ splitters are £170 - that's more than the N100 LOL. Would be cheaper to replace the Gigaset VoIP box with a PoE model to free an AC outlet on the UPS.
On the plus side my N100 came with a Delta Electronics PSU so it might actually be safe to use.