Remounting system on android emulator lasts about 10 seconds and reverses until reboot
I saw the exact same puzzling behavior. To remedy this, use the -writable-system option when you start the Android emulator.

eg:

~/Library/Android/sdk/tools/emulator @&lt;avd_device_name&gt; -writable-system

Issuing adb remount afterward should then allow you to push to /system until you reboot or remount read-only again.