Is it possible to recover disappeared constructed pieces / bases from single player servers?

Hello @snowghost, welcome to the community!

As you’re playing in singleplayer you could either restore an older backup if you have it on the PS Cloud or a portable drive, or set yourself as an admin and refund the items and materials lost.

It’s possible that the issue was caused by database corruption, did you experience any crashes in your previous session?

What messages did you get in the Event Log?