Had 3/4" site finished hardwoods (3 1/4" wide) installed in a new home in late 2017. Been fighting the builder rep ever since re the excessive gaps, raised ends, etc. Just had an inspector determine that across I-beam joists (over basement) spanning 24", they used 23/32" OSB sub flooring. There are dips in excess of 1/2" to 7/8" across a 3' span. Nailing was inadequate to say the least. He estimates about 70% of fasteners required were used. Many spans over 10-12" between fasteners. Trying to get the 2-10 warranty to cover the replacement as he believes repairs aren't feasible, so doing all I can to make my case. Local city code is my main question. They use 2012 IRC for guidelines which have a table that I don't understand. For "species group" 1, it says 3/4' sub floor is required, for "species group" 2 & 3, it says 7/8" is required, and for "species group" 4, 1" is required. Is this talking about carpet, hardwood, tile, etc? I already know that NWFA says 7/8" is recommended, but having another piece of ammo that they didn't even meet code, might help.
Thanks,
Saw

Some sub-floor systems require a 3/4 finished floor installed over the floor sheathing.
If you are getting dips and bumps in the sub-floor it may be because there were no gaps at the ends of the panels. When the sheathing expands the excess length could cause a bow. This would come from excess moisture.
Installing a wood floor without proper sub-floor preparation, including making the sub-floor flat to within the recommended specifications seems to be your problem that needs addressing. The fastener spacing is another problem. 8-12 inches between fasteners is OK. Each board needs minimum of 2 fasteners, one fastener within 3 inches of each of the board ends.