Hi and thanks for all your feedback. I will be going through it gradually!

This is actually a 'feature' of network manager version 1.2 onwards so there isn't a lot I can do about it.

A small excerpt from that blog post:

The VPN support has been improved considerably too. Before NetworkManager 1.2 users could only run one instance of a particular VPN plugin that would service exactly one connection. This limitation is now gone.

That's my bad. Apologies for wasting your time.

But that's a pretty stupid improvement. If it doesn't check that the new connection is usable.
It didn't matter which of the two VPN connections I disconnected. Both would disappear, taking with them all other VPN connections. Only the connection to the tangible NIC was left (visible) and disconnected. As soon as I connected to that one, the default nl VPN was also connected and took over, and the other VPN connections would appear again.

I agree that it's implemented in a very unintuitive way.

I will keep this open for now, in-case it causes confusion for others and in-case there's a possibility for me to create a workaround to avoid the annoying behaviour in conjunction with nordnm.

Just for the record. I left NordVPN in favour of Perfect Privacy.

I have began working on support for other VPN providers, so keep your eyes open on issue #57 if you're interested in using this tool for whatever provider you choose!

In that issue, it would also be useful to hear what providers users would be interested in having support for, so I know which to prioritise.