burning smell

I have ipad pro which I used for an year. It smells slight burning sometimes. I put the plastic cover on my ipad just after I bought it.

I brought it to genius bar, and a staff member found white powder stuff between the apple logo and the cover, but test results including temperature was all good. He said my ipad is ok to use.

Now I am at home and I am feeling something is definitely wrong with my ipad. Since I have never removed the cover, white powder stuff came from inside of ipad. The stuff member successfully wiped out most of white powder stuff, but when I checked apple logo carefully I found slight permanent mark on the logo and the plastic cover. I believe something came out through logo mark and damaged apple logo and cover. Since white powder stuff looks like powder of old battery, this looks a battery issue.

Is ipad pro safe to use since it passed genius bar test? Or how do I resolve the issue if my ipad has issue?