Custom Connector failing on refreshing data with multiple calls to get a refresh token

from Microsoft oauth flow - return of a new token refresh:

When you refresh your token a new token is generated that is the default. 

i tried on my side and the BPI is sending and saving the correct token. 

try to implement the advanced OAuth Handling authentication for Power Query connectors - Power Query | Microsoft Docs

here is my implementation 

redirect_uri = "https://oauth.powerbi.com/views/oauthredirect.html"; // needs to be added as valid redirect URL (Desktop App --> PKCE!) 
logout_uri = "https://login.microsoftonline.com/logout.srf";
baseAuthentificationURL = (tenant) => "https://login.microsoftonline.com/" & tenant & "/oauth2/v2.0";
windowWidth = 1200;
windowHeight = 1000;

//OpenID method to get token endpoints on demand. 
openIDconfig = (dataSourcePath) =>
    let 
        //host = Uri.Parts(dataSourcePath)[Host],
        queryURL = "https://login.microsoftonline.com/" & Settings(dataSourcePath)[tenantName] & "/v2.0/.well-known/openid-configuration",
        queryString =  [],
        response = Web.Contents(queryURL, [
            Headers = [
                #"Accept" = "application/json"
            ],
            ManualStatusHandling = {400} 
        ]),
        body = Json.Document(response),
        result = if (Record.HasFields(body, {"error", "error_description"})) then 
                    error Error.Record(body[error], body[error_description], body)
                 else
                    body
    in
        result;

//will be called as first function on login. 
StartLogin = (clientApplication, dataSourcePath, state, display)  =>
    try
        let
            codeVerifier = Text.NewGuid() & Text.NewGuid(), //needed for PKCE this will remove the need for a client secret.
            authorization_endpoint = openIDconfig(dataSourcePath)[authorization_endpoint],
            AuthorizeUrl =  authorization_endpoint & "?" & Uri.BuildQueryString([
                client_id = Settings(dataSourcePath)[client_id],
                redirect_uri = redirect_uri,
                response_type = "code",
                code_challenge_method = "plain", //needed for PKCE
                code_challenge = codeVerifier, //needed for PKCE
                scope=Settings(dataSourcePath)[client_id] & "/user_impersonation offline_access" //only if offline_access is requested a refresh_token is provided.
                ])

        in
        [
            LoginUri = AuthorizeUrl,
            CallbackUri = redirect_uri,
            WindowHeight = windowHeight,
            WindowWidth = windowWidth,
            Context = codeVerifier
        ]
    otherwise
        let
            message = Text.Format("Start Login Methode Error")
        in
            Diagnostics.Trace(TraceLevel.Error, message, () => error message, true)
;
//after the user has done the MFA this function will be called
FinishLogin = (clientApplication, dataSourcePath, context, callbackUri, state) =>
    let
        parts = Uri.Parts(callbackUri)[Query],
        result = if (Record.HasFields(parts, {"error", "error_description"})) then 
                    error Error.Record(parts[error], parts[error_description], parts)
                 else
                    TokenMethod(dataSourcePath, "authorization_code", parts[code], context)
    in
        result
;

//in the case of first login or token refresh this function will be called and request an (new) access token
TokenMethod = (dataSourcePath, grant_type, tokenFieldValue, optional verifier) =>
    let
        codeVerifier = if (verifier <> null) then [code_verifier = verifier] else [],
        codeParameter = if (grant_type = "authorization_code") then [ code = tokenFieldValue ] else [ refresh_token = tokenFieldValue ],
        queryString = codeVerifier & codeParameter & [
            client_id = Settings(dataSourcePath)[client_id],
            grant_type = grant_type,
            redirect_uri = redirect_uri
        ],
        token_endpoint = openIDconfig(dataSourcePath)[token_endpoint],
        tokenResponse = Web.Contents(token_endpoint, [
            Content = Text.ToBinary(Uri.BuildQueryString(queryString)),
            Headers = [
                #"Content-type" = "application/x-www-form-urlencoded",
                #"Accept" = "application/json"
            ],
            ManualStatusHandling = {400} 
        ]),
        body = Json.Document(tokenResponse),
        result = if (Record.HasFields(body, {"error", "error_description"})) then 
                    error Error.Record(body[error], body[error_description], body)
                 else
                    body
    in
        result;

//Called on token experation
Refresh = (clientApplication, dataSourcePath, oldCredential) => 
    let 
        refreshToken = oldCredential[refresh_token],
        result = TokenMethod(dataSourcePath, "refresh_token", refreshToken)
    in
        result;

//Called on Logout
Logout = (clientApplication, dataSourcePath, accessToken) => logout_uri;