Hi,
I was finally able to replicate this, there have also been some other reports;
I was testing on a series x (and further tests on PS5), It only appears to currently occur in single player sessions.
I was able to replicate the issue by selecting in admin mode “no building cost”, and “no sprint cost” prior to any attempt at picking up any building pieces.
I was then unable to return any pieces, and as stated the option was completely gone from my radial menu.
However, I was able to find a solution to the issue on both platforms.
XBOX Series X:
I quit to dashboard, and deleted the local save game.
My Games & Apps > See All > Games > Conan Exiles > Manage Games & Add ons > Saved Data > Delete All (DO NOT SELECT DELETE EVERYWHERE)
Then loaded in (from synced cloud storage), and pickup was restored. I was also unable to replicate again.
PS5
Settings > Games/ Apps & Saved Data > Saved Data PS4 > Cloud Storage > Download to system Storage > Conan Exiles
PS4 (Untested so backup to USB if possible before attempting):
Settings > Application Saved Data Management > Saved Data in Online Storage> Download to System Storage > Conan Exiles> Single Player/ Coop Game Data
Hope that helps!