Before installing cos mod 12.1:
1. Removing apps from Recents also kills background services of apps like WhatsApp, Hike, etc., which prevents notifications from being received until these apps are manually opened again.
2. User-installed apps like WhatsApp do not auto-start on boot. So no notifications are received until the app is opened manually.
3. Very often, the brightness of the display automatically changes to maximum even when auto-brightness is off. This can hurt the eyes when it happens while the phone is being used in a dark environment. Manually re-setting the brightness to low only leads to 'auto-max-brightness' happening again soon after. This seems to be caused by PowerManagerService or DisplayPowerManager.
4. Boot Animation doesn't play properly in many cases.
5. "Apps with usage access" feature in Security is reported to be not working.
6. Apps like True Caller, App Lock, etc. are not working, probably due to bug number 5.
7. UC Browser if storage is set to external sd card, the downloads will get failed in a sec or two.
8. Battery backup was too less even on wifi.
9. Camera sound cannot be disabled, not even by enabling "No Interruptions" ring mode.
10. While in a call half screen is coming with caller name and half is dialpad. There is no option to receive/reject the call... After finished I've to call back to the same no, with this same halfscreen problem...
11.Cannot set another browser as default browser, unless root the phone and uninstall stock browser.
So I was waiting eagerly for an update or cyanogen mod (I'm first time using it now). Then I read a thread on yu forum redirecting here for cos12.1. I have already unlocked bootloader on my device and proceeded further with the above steps. And ye I asked in my previous post about those cmds to be entered together at once or separately. It have to entered separately, though most of the above cmds took barely 1-30 secs but system.img took like 3 mins. I was really worried if it was stuck or something or bricked my phone. But the flashing completed in 1 hour.
Now feeling cool without any those above bugs, whatsapp works good and truecaller is already intregated into rom, which doesn't require us to download truecaller app.
Though a bit more work have to be done, like first booting twrp, then install supersu, then xposedframework then no watermark module.
Phone is running smooth and fast, no lags. So ye it got improved by getting cos.
Loving it <3