This issue can happen for Magento Cloud customers who trigger Blackfire builds at each deployment.
This means that at least step 3 of the configuration guide for Magento Cloud has been successfully completed.
Solving the issue
For each Blackfire environment you're working with for the Magento Cloud project:
Browse to its "builds" tab
Click on the "i" icon next to Magento Cloud in the integrations list
Open the advanced settings
Scroll down to and check the "Disable SSL certificates verification" option, then Save the settings.
User journey as below: