Ran into the same issue today after updating plugins with a Sage 10 project…
The reason for us was an update to the BackWPUp-plugin and pinning it to v4.0.0 resolved the issue for now.
"wpackagist-plugin/backwpup": "4.0.0"
Of course this is very specific to our setup / usage but I wanted to give a heads-up and point anybody towards checking for recent plugin updates and incompatibilities.