Hello,
Thanks for the advice.
I purposely added a lot of books/fics to my reader & once ejected immediately plugged it in to my Samsung phone charger.
I've done it twice now & so far, so good.
Before I've either leave it unplugged after ejecting or, plug it back into the laptop/PC, but the problem still happened.
Silly me, I knew that powering from a computer doesn't give so much power as plugging it into the wall, but my brain didn't put it all together in this case
Thank you all for your help