This is written in the super node's operation manual.
Open TCP inbound/outbound ports for 7778, 7880, and 7890 on firewalls and routers
Many people think that Port 7778 is used by light wallet, but it is also used normally by NanoWallet.
Certainly there may be a difference between the function of the super node and the function to be provided to the client, but if we are using an SN that does not satisfy this condition (non Open 7778) SN, the NanoWallet multisig signature request is notified It will not be used.
As another matter, if you are watching various SNs, there are also SNs that you set for yourself only, with 1 empty slot providing DeligateHarvesting. I do not think that this will be a big problem because there is no rule (feeling, ???).
Currently, this problem seems to be low priority, but I will recommend as a matter to be improved in the future.