Just recreating (rather then upgrading) my own little site to V13.0.1. It's running but for every page request (front end or back office) I get the following error in the dotnet console:- `[16:57:51 WRN] Error unprotecting the session cookie. System.Security.Cryptography.CryptographicException: The payload was invalid. For more information go to https://aka.ms/aspnet/dataprotectionwarning at Microsoft.AspNetCore.DataProtection.Managed.ManagedAuthenticatedEncryptor.Decrypt(ArraySegment`1 protectedPayload, ArraySegment`1 additionalAuthenticatedData) at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.UnprotectCore(Byte[] protectedData, Boolean allowOperationsOnRevokedKeys, UnprotectStatus& status) at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.Unprotect(Byte[] protectedData) at Microsoft.AspNetCore.Session.CookieProtection.Unprotect(IDataProtector protector, String protectedText, ILogger logger)` I'm running on Linux Mint with no TLS cert (cos it's too mind bending to sort out!). Do people see this on Windows too? Also the Umbraco log is filling up with "Error uprotecting the section cookie" Warnings and "Keep alive failed at ("http://localhost:1234/api/keepalive/ping") Errors, like over 1,000 of them in a couple of hours. This is on my dev machine, not a live site. Any advice appreciated.

Does this error show up in a brand new install on the same environment?

Yes, even with a blank install. Just opening anything, including the login page, causes the warning.

I’ve not looked for it yet. Will check when I’m back at my desk