We too are getting this error: "The survey does not exist or is not accessible".
The problem occurs on a recently updated survey that works fine in the mobile app, successfully adding and submitting records. The form and the data are not accessible on the Survey123 website. The hosted feature service is functioning properly and accessible.
This same issue has reoccurred with older surveys based on earlier versions of the same basic survey design. Surveys that have not been modified at all suddently stopped being accessible via the S123 website, perhaps due to website updates.
All of the surveys with issues were designed on a somewhat outdated release of S123 and S123 Connect. The reason we have been holding off on upgrades is because it appears that there is no .msi installer for these products on Windows, which is what our IT department requires for frequent updates for products that are changing quickly like S123.
We could just create a new survey and migrate the 5k records as a workaround, but it sure would be nice to avoid this issue in the future.
Thanks