I am going to say, right off the bat, that the reason your recipe is not working out well is because the corn syrup addition and quite possible the egg multiplication. First, just adding and ingredient like corn syrup, is a no no unless you have compensated on all the other ingredients. I do have other posts trying to explain the whys and the hows on the science of baking but it essentially comes down to, you CANNOT omit one ingredient nor ADD an ingredient to a baking recipe without the proper adjustments of the other ingredients within that recipe.
3. I havent cut back on the sugar... I will look into that. I only use brown sugar and a small amount of light corn syrup. I eliminated white sugar to make them softer. (when making a "single" batch they turn out fine) I know that too much corn syrup can cause it. So maybe thats still the culprit.
If the original recipe called for granulated white sugar and you just substituted corn syrup for it instead without the proper adjustments to your recipe then when you try to make a larger batch......this is where you will go wrong. Once again, you CANNOT do that. If you would like to make your cookies softer I would suggest adding a wee bit of cornstarch to your recipe to get you the results you are looking for. It makes the cookies beautiful, soft and melt in your mouth without compromising on flavour or structure.
An all butter batch of cookies whether it is a small batch or a very large one makes no difference in the spread outcome in the end if all the other ingredients have been properly adjusted according to the weight/volume of the original recipe. I have made and baked 100's of thousands if not millions of all butter cookies in my career both very large and small batches and NEVER had to compensate nor substitute for the all butter within the recipe. Sometimes it has to do with the liquid from the eggs, as most people forget to weigh the ingredients and just multiply the eggs as a whole rather than understanding that eggs are a naturally formed ingredient which makes it prone to weight differently once removed from the shell almost every time. (and yes you can use whole eggs as you will be weighing all ingredients anyway) Or, as you all have pointed out sometimes it has to do with the leavening not properly adjusted. However, MOST of the time it is because ALL the ingredients have not been properly figured accordingly.
What @Luc_H above and the others have said is correct. In baking, in order to multiply a recipe properly and get the best results, you must weigh each ingredient in the 1X recipe individually first to get the weight/volume equivalent. Just to give you an idea as to why, 1 cup of brown sugar (220g/8oz) is NOT identical to 1 cup of granulated white sugar (200g/7oz) in weight. Also, 1 tsp of salt (~6g) does not weight the equivalent as 1 tsp of baking powder (~4g). So this is why we weight every ingredient in an original (1X) recipe out first in order to have the proper understanding of what ingredients we need to adjust when we multiply. I always weight in grams as trying to figure 1 tsp of anything into ounces is not gonna happen.
Ok so no I literally just did it by volume. (example 2 cups flour x 8 for 16 cups) yikes is that wrong then? I should have weighed the base amount (single batch) first..... I am such a newb lol
So for example.....in your recipe you have stated that there are 2 cups flour (I am going to assume all-purpose). 1 cup of all-purpose spooned into the cup not scooped (also a no-no) is approximately 140g/5oz so 2 cups will be approximately 280g/10oz. Now you can see that it is not as simple as just saying 2 cups flour times 8 equals because the baking recipe will turn out wrong. However, if you weigh the ingredient (flour 2 cups=280g10oz x 8 = 2240g/80oz) now you have the exact measurement for that ingredient instead of 16 cups you will actually need 18 cups and 1 tbsp of flour. Now your baking proper!
Using parchment paper is perfect. Also, as the others have said, chilling the dough is essential. I scoop portioned balls of dough onto my prepared pan, freeze the portioned balls of dough on the sheet and then store them in labelled containers in my freezer. That way I can take as many prepared frozen cookie dough portions out according to my production baking schedule and bake fresh.