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Did you uninstall the old version of any v2 before installing v2.1? If you didn't, please do and give your feedback.

I did otherwise and restarted my phone....for now it is smooth

We do test incremental upgrades but if you upgrade from very old version there might be unknown issues, because we keep improving app, adding new features, changing how data is handled so that its performance can be best as well as user experience. Reinstalling @horpey suggested might solve your issue, let me know otherwise 😉

Finally I have uninstall to.indtall again.

Let see how it works. I saw you mentioned build number 1648 ...
But I am getting 1646 @good-karma

It might be because of Google Playstore update delay. Give it few minutes or hour and check again, please. But update from 1646 to 1648 should be fine, 1648 has small bug fix, good to update when you see it is available