REST client errors with vAPI endpoint

Just wanted to run this by the community to see if anyone observed this in their environments (vRO 7.2/vCenter 6.5)

Getting this error intermittently and not able to simulate on demand:

Status code 500

{"type":"com.vmware.vapi.std.errors.internal_server_error","value":{"messages":[{"args":["Rejecting login on a session where login failed"],"default_message":"Provider method implementation threw unexpected exception: Rejecting login on a session where login failed","id":"vapi.bindings.method.impl.unexpected"}]}} (Dynamic Script Module name : promiseTagCategory#74)

Line 74 would be this:

function getTagCategories(restHost,sessionID) {

    var request = restHost.createRequest("GET", "/com/vmware/cis/tagging/category");

    request.setHeader("vmware-api-session-id",sessionID);

    var response = request.execute();

    if (response.statusCode != 200) throw "Status code " + response.statusCode + "\n" + response.contentAsString;

    // Returning an array of tag category ids

    return (JSON.parse(response.contentAsString)).value;

}

Sounds like server side is the culprit but I am not certain what to look for on vCenter to debug further.