Unable to open project properties

I have problem opening Project properties in Node red. I see this error in browse console:

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I have tried to open Node Red in Chrome and Edge, but the error is the same. What should I try?

Have you installed any new nodes recently?
Have you tried restarting Node RED?

Yes, i have installed one node which is not in the node-red library. The Node works ok. I have Also tried to restart node Red with no sucess. Should I try to remove the new Node from the flow, restart node Red and check the project properties ? Or IT does not matter if the Node is in the flow or not, if its installed in Palette ?

If all is working, then you do something, and something else stops working, it is always worth undoing the change if possible to see if that is the cause.

I had this when I made manual modifications to the project's package.json.
I thought used nodes had to be declared there as opposed to the /data/package.json.