https://linux-tc-notes.sourceforge.net/tc/doc/cls_u32.txt:
The base operation of the u32 filter is actually very simple. It extracts a bit field from a 32 bit word in the packet, and if it is equal to a value supplied by you it has a match. The 32 bit word must lie at a 32 bit boundary.
There is no central naming authority in I2P. All hostnames are local. (Naming and Address Book)
Therefore, if an url doesn't work, it isn't in your local address book.
You can add mappings yourself if you know the destination or b32 address, or make use of subscriptions. In this case, add http://i2p-projekt.i2p/hosts.txt and http://notbob.i2p/hosts.txt to your address book subscriptions, the latter contains the destination for mysu.i2p.
Yes this is sane and one of the main use cases for encrypted lease sets. Encrypted lease sets make it impossible for unauthorized users to connect to your hidden services.
If you know beforehand that only one client needs to be able to connect, choose "DH" as a security strategy, and share the client's key with the server. This article explains these concepts in detail.
If you don't care about anonymity (given the 0-hop tunnels), you could also stick both hosts on an overlay network like Yggdrasil. This may or may not be more convenient / performant based on the number of services you want to expose.
You should not torrent over the tor network, but you can torrent over the I2P network. qBittorrent even has experimental I2P support built in.
Have you tried running tcpdump / wireshark on another device in the network when this happened?
Edit
i2psnark.upbw.maxini2psnark.config(this can be in a number of locations based on install type and platform - just search for it).Or you can remove the
maxlengthandsizeattributes from the text input, it will save just fine.