Unable to save_as workflow due to File access problems Math Formula node (Access is denied)

Hi,

when trying to save a new version of my workflow I receive the following message:

File access problems: C:\Users\Me\Onedrive- …\Workflow\Math Formula (#863)\port_1(Access is denied)

This is a node that has not changed compared to the previously saved version.

I have even deleted the node but still get the same error message.

When I look in the workspace the workflow has been saved as a group instead of as a workflow.

Who can help?