You drained oil then ran comp test
If those gas ports work like how they should, you need some good cranking speed for it to shove the rings out. The low/no oil shouldn't be an issue, if you hit the cyl with oil and compression comes up considerably, good sign rings are toast. Did you remove all the glow plugs and then test one at a time? Need to have a fairly high cranking speed.
Did you drag test the rings before assembly?
If those gas ports work like how they should, you need some good cranking speed for it to shove the rings out. The low/no oil shouldn't be an issue, if you hit the cyl with oil and compression comes up considerably, good sign rings are toast. Did you remove all the glow plugs and then test one at a time? Need to have a fairly high cranking speed.
Did you drag test the rings before assembly?