I am using PayPal Express plugin. Thanks for reply! The problem seems to be in PayPal itself, not the plugin, and not the settings that I mentioned here. PayPal simply sometimes display login form, and sometimes credit card payment form, depending on various factors like country of customer, cookies and cache in his browser and many more. This is answer I got from PayPal, so basically even they couldn't give me more precise answer, but their answer gave me idea to test this on other browsers/devices and it worked. So, in my case, it was probably something saved in the cookies.
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