Welcome to Q&A forum ~
But Visio online is not supported on Q&A forum currenlty, the tag "office-visio-itpro" focuses more on general issue of Visio desktop app.
To better help you, I would suggest you also post a new thread on following forum. Thanks for your understanding.
Microsoft Answers forum --- Visio
If conditions permit, I personally suggest you open these files on other computers with Windows system to check whether the files have any problems.
Besides, please chage other browsers to have check.
It's recommened to make sure the Pop-up Blocker for that site is turned off. If not, please disable Pop-up Blockers or add a Trusted Site.
Hope the information is helpful to you.
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