Will my existing Item Network SA save work?
Yes, with one loss. Your chests, tanks, sensors and the items inside them all survive, and each chest recovers its item and quality list on its own. What cannot survive is the contents of the shared network itself, plus the Request/Provide setting and limits on each chest. Empty your network into real chests and tanks before you switch.
Why can't you just read the old mod's data?
Factorio keys a mod's saved data to its internal mod name, and there is no supported way for one mod to read another's. The original also exposes no remote interface. This is a hard engine limit, not an oversight.
Why is everything set to Request after switching?
Because that is genuinely all the world knows. Chest requests are mirrored into the chest's inventory filters, which is how the item and quality list is recovered — but filters look identical for Request and Provide rows. Re-pick the mode on your provide chests.
Something dumped a load of items into the network, or pulled items out unexpectedly.
That is a recovered chest with the wrong mode. Nothing is lost; set it back to Provide (or Request) and the items go back where you want them.
Why is my network empty?
It could not be carried across. See the first question.
Is this abandoning the original?
No. It is a stopgap. If djmalk ships a 2.1 build this mod retires, and if he asks for it to come down, it comes down. He has been told that directly.
Can I use this and Item Network SA together?
No — they define the same entities, and the two Factorio versions are mutually exclusive anyway.
Multiplayer?
Works, but every player needs the same version, as always. Do the swap when nobody is mid-session.
What exactly changed from 1.0.3?
The 2.1 port itself is six edits across three files, plus fixes for the save-breaking crash and the quality bug, plus adoption of existing entities. Full detail, including what has not been tested: https://github.com/restjack/item-network-sa-continued/blob/continued/docs/PORT-NOTES.md
Found a bug?
Post in the discussion tab with the error text and your mod list. Both crashes fixed in 1.1.0 were diagnosed from reports on the original mod's page.