Loading a wallet from a state where only the default wallet was active results in using an empty string for the initial/default wallet name.
This is a GUI only quick-fix that overrides wallet(s) with name "" to "[default wallet]". Does not affect getwalletinfo or listwallets.
Also, unsure if it should be fixed at a deeper level and if – instead of [default wallet] – it should use wallet.dat (the filename of the default wallet).