React Is Not Defined Following Sanity Upgrade

Hello! I wonder if this is a known issue, I just upgraded an older project with

sanity upgrade

and now get
when I try to run it in the browser. The project really isn't complex but I can't seem to find the source of the problem.

Hi , could you check if there might be a missing React import in your schema definitions or custom components?
Alternatively, could you try removing your

node_modules

folder and

package-lock.json

+

yarn-lock.json

files before running

npm i

and trying once more to start the studio?

Thanks for the hint, I should have known better 😛 - it was a missing import on a custom plugin.