Hi,
you are using a Release Candidate version, not a stable version.
PleaSEW remove the installed c4doctane version and upgrade to 2021.1.4-R4 new stable version.
You can find it by visiting your personal Downloads area:
https://render.otoy.com/account/download_archive.php
Then copy paste everything in a new scene, and use the latest stable version to edit the scene.
ciao,
Beppe