Trying to troubleshoot frequent loose stools (raw diet)

My 13 month old pup Syrous has been having frequent bouts of diarrhea for the past few weeks, and I'm really having a tough time figuring out the root cause of it. I'll give some background:

He's been fed raw his whole life, and it's been always hit and miss with what would come out of him. He went from 3 meals to 2 to 1 per day as he lost interest in breakfast, so he's been getting 1.2 to 1.5lbs for dinner (he's a fit 37lbs and very active). The basis of his diet was almost always chicken backs and necks with something added in, either ground beef, whole mackerel, chicken thigh/wing, some tripe, raw egg with shell, or some combination of the above. For the last few weeks, however, he's had really bad runs. After speaking to a few other raw feeders, we thought that maybe he developed a sensitivity to chicken, so I cut out all chicken for a week or two and fed primarily ground beef chunks with some beef or lamb shank for bone, the odd turkey wing, and he was doing ok but still had some off days. I spoke to my holistic vet and he suggested for a week to feed him a commercial raw lamb diet that had a pre-determined ratio of bone to meat, along with organ meats, tripe, veggies and oils. On this (very expensive) diet his stools became almost perfect EXCEPT he would still get runny poo 2-3 hours after eating. He was only getting 1lb a day on this so now he's down to below 35 lbs and looking a touch skinny.

I'm really not sure what to think. There are a few possibilities in my mind, which I would like some input on.

1) I've never really gotten a grasp of the right ratios of bone to meat to organ - I understand the numbers, but I can't put those into actual meals. I have no idea what 20% bone looks like, for example. Perhaps he's never getting enough bone and/or he's getting too much of something else?

2) Why does he get runny poo 2-3 hrs after his meal, but the next morning and afternoon it's perfectly fine? Could it be too much food in one sitting? He'll eat as much as I give him regardless of quantity, but he isn't keen on having his meal split into morning/night...

3) What are the signs that he could be sensitive to certain proteins ie. chicken? Is there any way to tell what's going on by the colour or consistency of his stools?

In my freezer I have chicken carcasses, chicken quarters, chicken hearts/gizzards, chicken feet, fine ground beef, chunkier beef chunks, beef organs (mix of heart/liver/kidney, etc), beef and lamb shank (thin boney ribs), whole mackerel, and ground chicken with and without bone in it (all of this is from a supplier who specializes in raw pet food). Can anyone suggest some good proportions of what to feed from the above selection to give, say, a 1.25 lb meal? What additional additives would be recommended? I have fish oil and coconut oil which I also add on occasion, and I can add canned pumpkin, though I haven't had much luck with that. Mind you, I might have always just had my meat to bone ratio completely off this whole time... I'm just at my wits end here! Help!!

Aww poor syrous, I hope you manage to get it sorted out, I've no raw experience but we have some raw feeders one of whom should be along shortly to help

Perhaps having a read through this topic may help

https://staffy-bull-terrier.niceboard.com/t19197p375-what-s-in-the-bowl-today-graphic-photos-raw#628843

I would lean towards a sensitivity to poultry in general (Dempsey has this as well), but I would also advise you to try splitting his food into two or three smaller meals to see if that makes a difference. With some dogs, if they eat too much in one sitting their digestive system can't cope and so much of it comes out the other end. It's watery because it's been broken down by the stomach acids, but the water content hasn't been absorbed by the intestines.

Try and stick to one meat source at a time for at least 3 or 4 weeks to try and rule out sensitivities.

I don't weigh out food, but go by the general rule that if there's too much bone your dog's poo will be hard & possibly chalky and if there's not enough bone it'll be soft.