Usually you progress - 60 / 80 / 100 / 120 - I'm not a flooring expert - but 60 is too coarse.

Also he is skipping more than 2 grit between cuts, a no no . Should be finished with least 80grit

I agree 80 at least, same as soapstone

35,50,80 or 40, 60, 80-100.

Thanks guys. Sure enough, there were 3 places where there were visible swirl marks after the stain. GC agrees it needs to be fixed. We'll see what I come home to today. I am getting pretty tired of having to inspect the work of every sub :(

Bona Traffic HD clearly states the sanding requirements. The final cut must be 80 - 100 grit then multidisc 80-120 grit. The 60 is the MIDDLE grit level, not the end level. I would bet the 36 grit was the only disc/belt the person had in their truck.

https://www.bona.com/Global/Documents/United%20States/Technical%20Data%20Sheets/TDS%20BonaTraffic%20HD%20US.pdf

The application instructions for Bona Traffic HD are there for a reason. I have a STRONG suspicion the "sub" isn't a professional. S/he is just "a person with a hammer" who has been given the floor finishing as a task by the GC.

I would require a wood flooring professional on the job. Bona is VERY difficult to work with. It is SOOOOO difficult that a "training weekend" is required just to get a handle on this stuff (volunteer to do training...at their own expense). Without that training, this is going to be HELL on the floor-dude(ette). And when Bona goes wrong, it goes wrong in a HURRY. And there is no fix other than another sand/refinish.

60 grit surface finish will lead to premature wear. Manufacturer's instructions and guidelines supersedes NWFA guidelines. NWFA is the standard for quality. Your contractor is not following either.

Bona recommends up to 150 grit surface finish on some of their products before applying any finish.