Lump usage on long cooks

What happened here?

Friday afternoon I filled the firebox with lump after cleaning out the egg. I used both left over lump from the last smokes and new lump, all BGE lump. I put the plate setter in and added drip pans, then the grill and three 8.5lb pork shoulders. Turned the Digi ll on and set it for 250/200 and settled into a few cold beers and a cigar. I was concerned that the amount of meat and the additional drip pan was going to interfear with the air flow but it seemed like the flow of smoke was equal to any other smoke I had done with one shoulder.

I did notice some erratic swings in the fire temps which had me messing with the top damper and the sliding damper on the Digi ll. All seemed fine when I checked around 9PM and off to bed I went. The top damper was barely open and the slider was set about 3/4 open. At that time the cook was 5 hours old. I got up at 5am and found the roasts around 170 but the fire temp had dropped to 200. I opened the top and everything looked as it should and this and fully opening both the top damper and Digi ll slider seemed to kick start the fire back and the temp slowly went back to 250. It took about an hour for that to happen. It started droppping again but at this point the meat was showing around 180.

I decided decided to move them to the gas grill and see what was up with the fire as I had 3 chickens I wanted to do after the pork hit 200. I found that I was out of lump after 17 hours. Actually probably before and the temp was held by the heat of the egg and meat for a while. I got the pork up to the 190s on the gas grill (indirect) and removed them to the cooler for a few hours and the were fine.

Since I have never used more than 1/2 of the lump in previous 12+ hour smokes I am wondering why I was out. Did the fire have to work harder because there was more meat to cook? The overnight temps were in the 60s which isn't cold but it isn't like daytime 80s either. Did that do it? Was it just a combination of things? Just curious as I have another large cook scheduled for next month and if adding lump after half the cook is normal I better plan on it befor going to bed.

Thanks in advance for any advice;

Jack