But then I noted 'Whatsapp' folder as seen by android file manager contains only 'Media' folder, whereas to my Linux mounted drive I copied all folders, which gave me a clue. I've tried giving permissions before Whatsapp starting as advised in other answer, but to no success, restarted my phone - again no success.
Disclaimer: this solution is offered to those who as myself found this post via googling for 'whatsapp not restoring local backup', I have not changed my number.
