in the off chance that anyone might come across the same problem (though fairly unlikely i think)
i finally remembered that the last time i'd gone in to those options, i'd hit "buy now" on a book i didn't want to buy...and it sent me to set up credit card info, which i didn't want to provide, since i want to wait until i actually have a book i want to purchase. so i cancelled or x-ed out or something.
so apparently it didn't like me doing that. that's why i was getting servers errors.
my solution was to sign out of my kobo account after syncing my books, and sign back in. and go through the start up process. which made my sideloaded books fall off their bookshelves
but did solve my problem with connecting to the store server.
i guess it somehow messed up my signed in status when i refused to continue the book check out by entering credit info. shouldn't have happened, but at least solvable without factory resetting or anything.