IBM has announced that iFixes are available to update IBM Connections with the latest versions of APNS certificates used by the mobile app for Push notifications. Fixes are available for the latest CRs for 5.0 and 5.5 and both 6.0 CR3 and CR4. Please follow the link below to the IBM Technote which has links to the different downloads.
The current (or most recent) APNS certificates expire on July 21, 2019, so you've got about 90 days to get these downloaded and installed. The new certificates are good until April 30, 2020.
If you need some assistance, I can help out with this and other IBM Connections administrations issues.