I lost one chick my first hatch that did not internally pip either...movement until day 21 then nothing 

 So sad.
As far as saddle air sacs go I have never dealt with one but I have had a few chicks all of a sudden develop pretty big air sacs during lockdown, scary for sure but I just made sure to keep the humidity at a good % once they pipped so they didn't get shrink wrapped.
As far as my hatching goes....I feel the grey hairs. I had one come out with blood (more than usual) we figured it poked a blood vessel on pipping or twisting because the blood was all at back of egg when it came out and trailed a bit out of egg. I gave that one some electrolytes and looks good so far.
I have 3 with splayed legs....so we have yarn hobbles on those and they are enjoying their sense of freedom with the training wheels.
Lastly my possibly final chick popped out with a inflamed abdomen, possibly not fully absorbed yolk. I made a post to get some advice. So fingers crossed for the final baby. It is still pretty fresh and wet so I am just letting it rest while I figure out next steps for that one.
Two are still in eggs, but I have a bad feeling they have passed away. I had 23 in and the last two have not pipped yet...I quickly checked for heartbeat and couldn't hear anything when removing dry chicks earlier.