Allocating a particular network config to a specific network card on startup

When you created new connections, you did not assign what network card each connection should use, hence the changes after reboot. Even if you do assign the card, each of those will still have 2 active connections, as explained above, Linux can have multiple network connections with multiple IP addresses for a single network card.
Delete means delete.
You can also edit those, but you will still have 4 active connections for 2 network cards, hence "delete the created ones", not the default ones named "wired connection 1" and "wired connection 2", these two need to be edited and their name can also be changed to whatever makes it easier to discern.
This shows the default wired connections, in my case just one, double click each to edit.

Or, if this seems easier
-delete all wired connections
-create two new connections assigning each to a network card
This is the simplest way, so probably should have started with this!