New construction subfloor unlevel
For a 2' span from the adjacent joist on only half the width of the sheet, that block is more than adequate. If there are a half dozen framing nails in it it'll never move. You could park a piano there and it would hold. The key is the fasteners, not the height of the block.

Now, you mentioned an out-of-level condition and failed to explain where. (Edit: I see it now in a comment.) I'll assume that it's the end of the sheet over that block. If so, the block should be raised or shimmed to bring the sheet level with the others.