VSO REST API - TFS/Core/RestClient GetTeamMembers is not a function

I have a custom hub that calls the Rest API via VSS. The call to retrieve the list of team members are now encounter an error, .getTeamMembers results into the TypeError: coreRestClient.getTeamMembers is not a function

var coreRestClient = TfsCoreRestClient.getClient();

coreRestClient.getTeamMembers(TFSPROJECTID, TEAMPROJECTID).then(results => { /* code */ });

the code below that retrieves the list of teams is currently working.

coreRestClient.getTeams(TFSPROJECTID).then(results => { /* code */ });

The call getTeamMembers was working properly before. Were there any changes on the API? The API docs for the getTeamMembers seems to be the same. Calling the Rest API by issuing a HTTP GET request works fine as well.