OnePlus

For background on how these settings could relate to the performance of the Zenit app, Battery Optimization.

OnePlus devices use a modified version of Android which they call Oxygen. The OnePlus 5 and OnePlus 6 devices seem to have the most aggressive battery optimization that could affect the performance of the Zenit app.

OnePlus 5 and 6:

• Settings > Battery > Battery optimization and switch to the “All apps” list (Top menu) > Zenit > Don’t optimize.
• You may also turn battery optimization off entirely by going to System Settings > Apps > Gear Icon > Special Access > Battery Optimization.
• On some OnePlus phones there is also a feature called App Auto-Launch which essentially prevents apps from working in the background. Please disable it for Zenit to work properly:

NOTE: For their OnePlus 5 and OnePlus 6 devices, settings may get reset with firmware updates so you may need to re-enable these settings as regularly as those devices update their firmware. Though the OnePlus firmware updates download automatically, they require manual approval to actually install.

Other versions of OnePlus phones:

• Settings > Scroll down to the Device section > Battery > 3-dot menu icon at the top right of the screen > Aggressive Doze & App Hibernation option > Toggle off.
• Also disable Settings > Battery > Battery optimization > (three dots) > Enhanced optimization. This option may also be called Advanced optimization.