I noticed this myself when using the F5 debug mode. I narrowed down the offending setting to be always-show-lightning-protection. When enabled, it causes the described issues.

What happens?
When loading a 2.0 save in 2.1, terrain generated on Fulgora has dramatically more land than generated in 2.0, or generated in saves created in 2.1. So much more to the point where all islands can effectively be connected to each other with little issue.
Steps to reproduce

Start ...

I second this suggestion, especially when it comes to circuit wires. Circuit conditions are copied onto the entities, but without replacing circuit wires that might already be present, those wires could cause circuit conditions to behave in unexpected ways.

I did see that thread while searching, and it seems like the conclusion in that thread is "a newly added temporary stop should always replace the currently active stop", which I can definitely see as necessary and intentional.

The point of contention I'm running into is where those temporary stops ...

What happens?
When adding a temporary stop to a train by ctrl-clicking the map, if the currently active stop is a temporary stop, either from another ctrl-click or an interrupt, the new temporary stop is added after the active stop and any other temporary stops until the next permanent stop. This ...

What happens?
Buffer chests that cannot have their logistics requests fulfilled due to being full sometimes report their logistic requests, and sometimes don't.
Steps to reproduce

Build the following setup:
0eNrNU8tugzAQ/Jc9m4jwiBKkfkmEkIFNYtXYxDZpI8S ...