I am using WSO2 Identity Server 5.1.0 and configured ADFS as an Identity Provider using the management console. I tested the created IDP by selecting it in one of my service
To solve the issue I had to change some xml elements in the FederatedIdentityProviders like below.
<FederatedIdentityProviders>
<IdentityProvider>
<IdentityProviderName>adfs-idp</IdentityProviderName>
<IsEnabled>true</IsEnabled>
<FederatedAuthenticatorConfigs>
<FederatedAuthenticatorConfig>
<Name>SAMLSSOAuthenticator</Name>
<DisplayName>samlsso</DisplayName>
<IsEnabled>true</IsEnabled>
</FederatedAuthenticatorConfig>
</FederatedAuthenticatorConfigs>
<DefaultAuthenticatorConfig>SAMLSSOAuthenticator</DefaultAuthenticatorConfig>
</IdentityProvider>
</FederatedIdentityProviders>