Hi,

I have seen a number of threads relating to this issue but no definitive cause or fix. I was hoping someone may be able to help.

Background

I have a site running on version 7.15.3. Looking at the umbracoMigration table I can see that it started out on Umbraco 7.6.2 and had had the following upgrades:

• 7.6.3
• 7.7.4
• 7.9.2
• 7.10.4
• 7.15.3

The site uses Umbraco Forms and like Umbraco has been through an number of upgrades from 6.0.1 to 7.1.1

The site is hosted on Azure as an App Service and all fixes have been applied as defined here

Issue

Ever since the upgrade to 7.15.3 (via NuGet), I am getting random occurrences of "The Xml cache is corrupt. Use the Health Check data integrity dashboard to fix it."

• The Health Check shows everything is fine.
• The front end is YSOD, but /Umbraco is still accessible.
• The error can be fixed by visiting /umbraco/dialogs/republish.aspx?xml=true although this doesn't always seem to solve the issue.

The error often appears as soon as I publish the the site to Azure. Yet the publish pipeline has not been changed and everything worked fine before the upgrade.

I have two other Umbraco sites which have both sufferd from the same "Xml cache is corrupt" issue since they were upgraded to Umbraco version 7.15.3.

My initial thinking was that it was down to Azure switching the underlying hardware, rendering the umbraco.config inaccessible but I have all of the suggested fixes in place. I have also seen this behaviour when running the site locally - updating Umbraco Forms via NuGet results in the same error.

Questions

1. Is this an issue with 7.15.3?
2. Is it a result of multiple upgrades over the years?
3. Umbraco Forms?
4. Something else?

Thanks,

James