Hi @Nick Sheedy ,
I suggest you go to File- Account and provide the detail version information about Visio here:
And try to provide the screenshots about problem in Visio and PDF.
You can also try to repair Visio to reset Visio to default settings:
https://support.microsoft.com/en-gb/office/repair-an-office-application-7821d4b6-7c1d-4205-aa0e-a6b40c5bb88b
Try these methods and check the result.
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