Process Model publish error

Have you spotted this thread on the same topic? https://community.appian.com/discussions/f/process/918/am-getting-the-following-error-while-saving-the-model-any-idea-invalid-in The discussion is 9 years old though.

Have you checked and/or re-mapped all items under the data tab for all nodes?

If the issue is still not found, delete nodes one by one to see where the issue resides. Then inspect further.

Can you isolate the issue to a specific node? I'd suggest making a copy of your process model, then trying to delete one node at a time until the error stops occurring. That can help you isolate the node that has a problem and you can investigate doing the same thing within the node (e.g. remove inputs / configurations until the error stops occurring).