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Hi webbrewers3,
Currently, we cannot select classic experience as the default experience in tenant level. So you could try following the suggestions and using a PowerShell script to enable or disable the modern experience for a single site collection or for a list of site collections as provided by the SharePoint Modernization scanner.
Back to the original issue, we think the issue might be caused by the changes between April 24th and May 31st. Given the situation, we would like to confirm the following points:
1.Does the issue occur in all libraries or lists?
2.If you use the option "Return to classic SharePoint" and use Quick Edit, can it display correctly? After that, clicking Exit classic experience option, can you use Quick Edit successfully in modern view?
Regards,
Eli