@Digital Shamans -The behaviour you are experiencing does seem to hold true when using both Ctrl+Z or the undo button in the Miro interface, both in the browser and desktop app (at least in Chrome on Windows 64-bit).

I suspect retaining selection information on undo was never considered as the purpose of undo to revert a change and selecting objects does not change their state.

If you were not already familiar with the shortcut, and your nodes are fairly close together, you could use Shift+drag rather than Ctrl/Cmd+click to multi-select the nodes again. 

If you would like for Miro consider making this a better user experience, I’d recommend adding “Remember object selections on Undo” as an Idea in the Wish List category.

If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.

Lastly, don't forget to vote for your own Idea.

You can Vote for the Idea here https://community.miro.com/wish-list-32/don-t-loose-object-selection-after-un-do-action-554