Sampler track is lacking a crucial feature for editing synced envelopes - fixed mode (Moving a node does not move the following nodes) - which is available with Groove Agent 5 SE. Without it,when editing the nodes, it is constantly required to readjust the other, non edited, nodes, which makes the whole process cumbersome.
Please implement the fixed mode in the next maintenance update - not in Cubase 11.5.
Haven’t tested 11 yet,
Can you shift select the nodes?
Not sure what you mean.
Hold ‘Shift’ on your keyboard, and then mouse click each node.
It just increases the precision of mouse movement.
But you can select multiple nodes by mouse dragging, if that’s what you’re going for.
Maybe make a GIF animation using LiceCap to display exactly what you are talking about.
Ad 1. When you hold shift and click on a node - it just selects the node. When you hold shift while moving a node, the movement is slowed down thus making it more precise.
Ad 2. You can select multiple nodes by mouse click on empty space + drag selecting the nodes.
Does this resolve your problem though?
Not at all. 
Thanks for your attempt to help, though.
From Groove Agent SE manual (Editing Envelopes):
"Fixed
If Fixed is activated and you move selected nodes on the time axis, only the selected nodes are moved.
If Fixed is deactivated, all nodes that follow the edited nodes are also moved."
Current behaviour in sampler track is:
“If Fixed is deactivated, all nodes that follow the edited nodes are also moved.”
And I want editing to have the other behaviour.