Synchronizing the Add-In content in Excel Online and Excel Desktop
I created a new Excel file in Excel-Online and then additionally opened the file in Excel Desktop, so that both are open in parallel. When, for example, I edit cells, these edits are synchronized between the files. That's fine. In the online version, I added the Visio Data Visualizer from the Add-Ins. This worked and the Add-In pane/shape also immediately appears in the file opened in Excel Desktop.
I selected a basic flowchart in the file opened in Excel Online. The Add-In inserted a table and shows the diagramm. But that is not (!) synchronized with the same file open in Excel Desktop. I can select another diagramm (e.g. a cross functional chart) in Excel Desktop and I get another table inserted to the file. So, I have now 2 tables. The same shape refers to 2 different tables in the file. If I refresh the diagrams in each Excel version, nothing changes. The Visio Data Visualizer Add-In also created to files in my One Drive folder, interestingly not in the folder "Visio Data Visualizer" but in my One Drive root folder.
If I close the file in Excel Desktop and Excel Online and then reopen it, I get the visio diagramm which has been lastly saved and they are then synchronized. My suggestion is to have the Add-In content data synchronized at least when a saving occurs.
I have made two screenshots, which are available here.