Which version of Visio are you using now?
Please go to File > Account > Product Information > About Visio.
I suggest go to
Control Panel > Programs and Features, find the Visio, right click it, and choose Change to perform a Online Repair or Repair for Visio.
In addintion, please go to Program Files\Microsoft Office\Office<version>\Visio Content\<Locale ID>, such as for my 64-bit Visio Plan 2 which uses English, I need to locate to
C:\Program Files\Microsoft Office\root\Office16\Visio Content\1033, find the Gantt templates as following image shows, open them directly to have a look.
If it still does not work, maybe you could try to replace these Gantt templates with these templates from other normal PC.
Any updates, please let me know.
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