Meizu is probably on par with Huawei and Xiaomi in their approach to background process limitations, but they get a better rank probably just because those devices are not that common on the market, and thus do not cause such pain to the developers as the aforementioned.
Adjust your settings:
Device Settings > Advanced Settings > Battery manager > Power plan set to Performance
Device Settings > Advanced Settings > Battery Manager > Protected apps – check Pomodoro app as Protected
Enable Device Settings > Apps > your app > Battery > Power-intensive prompt and Keep running after screen off