That's a notification originating from the Data Saver feature in Huawei ROMs (EMUI 5.0).
Data saver helps to reduce data usage by preventing background apps from sending or receiving data and limiting the data access frequency of running apps.
When data saver is active, a data icon with a leaf will appear in the
status bar. This may prevent users from receiving updates from emails,
chat and other social media apps, and images will only be displayed
when you touch them. To enable the data saver mode, go to Settings ->
Mobile data -> Data saver.
Source: First view of EMUI 5.0 ROM: Android 7