As of 08.03.2018, the APNS Certificate used by Traveler 188.8.131.52 will expire and will not be valid anymore. For everybody who is running Traveler 184.108.40.206 this is a good time to update to a newer version. The current version of IBM Notes Traveler is 220.127.116.11.
You can also update the certificate files, as Detlev described in his blog post.
Why is APNS Certificate important? IBM Technical Support Video