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Some memory fragments can't be placed where they look like they should. For example, glacial cavern has bridges on the topleft, topright and bottomright. but for some reason I can't connect it to the nexus at all. there should be 3 ways to plug it in, but none of them show up. This also happens sometimes trying to connect things to other pieces, so it's not just a bug related to the nexus.

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about 5 years ago - /u/chris_wilson - Direct link

To place a piece, you need to click on one of the interactable objects on the appropriate bridge in the Memory Nexus.

Once you have placed your first piece, you'll be able to use "planning mode" from anywhere (which marks the pieces as queued to place automatically when you go to that bridge).