Get Error "IDX10511: Signature validation failed" when trying to validate an Azure AD token

I have an Angular 10 application that authenticates with Azure AD using oidc. It successfully gets the token and then makes a REST call to a WCF service (.net framework 4.7) sending the token it received from Azure. The validation code in the WCF Service fails with the following error: IDX10511: Signature validation failed. Keys tried: 'System.Text.StringBuilder'. kid: 'System.String'. Exceptions caught: 'System.Text.StringBuilder'. token: 'System.IdentityModel.Tokens.Jwt.JwtSecurityToken'.

If I authenticate using Auth0, the same WCF code is able to validate the jwt from Auth0 with no errors.

Below is the UserManagerSettings for my oidc client:

          this.stsSettings = {
            authority: "https://login.microsoftonline.com",
            client_id: myclientId,
            redirect_uri: `${myclientRoot}signin-callback`,
            scope: "openid profile email",
            response_type: "code",
            loadUserInfo: false, // setting loadUserInfo to true causes error because CORS blocks the call to the user info endpoint.
            post_logout_redirect_uri: `${myclientRoot}signout-callback`,
            silent_redirect_uri: `${myclientRoot}assets/silent-callback.html`,
            metadata: {
              issuer: `${mystsAuthority}/${mytenantId}/v2.0`,
              authorization_endpoint: `${mystsAuthority}/${mytenantId}/oauth2/v2.0/authorize`,
              token_endpoint: `${mystsAuthority}/${mytenantId}/oauth2/v2.0/token`,
              "jwks_uri": `https://login.microsoftonline.com/${mytenantId}/discovery/v2.0/keys`,
            }

My C# code in the WCF Service to validate the token

                JwtSecurityTokenHandler tokenHandler = new JwtSecurityTokenHandler();

                JwtSecurityToken jwtToken = tokenHandler.ReadToken(token) as JwtSecurityToken;

                if (jwtToken == null)
                {
                    return null;
                }


                IConfigurationManager<OpenIdConnectConfiguration> configurationManager = new ConfigurationManager<OpenIdConnectConfiguration>($"{Properties.Settings.Default.ValidIssuer.TrimEnd('/')}/.well-known/openid-configuration", new OpenIdConnectConfigurationRetriever());

                OpenIdConnectConfiguration openIdConfig = await configurationManager.GetConfigurationAsync(CancellationToken.None);

                var validationParameters = new TokenValidationParameters()
                {
                    LifetimeValidator = LifetimeValidator,
                    ValidAudiences = new[] { Properties.Settings.Default.CommaDelimitedValidAudiences },
                    AudienceValidator = AudienceValidator,
                    ValidIssuer = Properties.Settings.Default.ValidIssuer,
                    ValidateLifetime = true,
                    RequireExpirationTime = true,
                    ValidateIssuer = true,
                    ValidateAudience = true,
                    ValidateIssuerSigningKey = false,
                    IssuerSigningKeys = openIdConfig.SigningKeys,
                    RequireSignedTokens = false
                };

                SecurityToken securityToken;
                var principal = tokenHandler.ValidateToken(token, validationParameters, out securityToken);

                return principal;
            }

            catch (Exception ex)
            {
                return null;
            }

The exception occurs at the code tokenHandler.ValidateToken(token, validationParameters, out securityToken);

I tried various online suggestions, adding a scope in Azure, the workaround for "a 0 byte prefix.", etc and they didn't work.

I've been on this too long and am running out of ideas.

Please help.

Thanks,