Hi there!
Thanks for contacting us.
If you have this problem for all the newly to be compressed images, can you please make sure to have set the right API key in your media settings (Settings >> Media). If you do have the correct API ket set in your settings, please try and reset your API key in your account dashboard here: tinypng.com. Once you have reset your API key, use the new key in your media settings.
If you are still experiencing issues after this, please contact us on [email protected] and we will investigate further!