It is good you have been considering various factors.... from bowls, underlying health to stress & depression.
As well as full bloods I would probably have a full worm count done too.
I am assuming as not mentioned there aren't any obvious physical presentations. I am mindful it is difficult to feel over for lumos bumps distortions on a dog with a heavy thick coat.
I haven't seen comments re worming/flea treatments...I have my personal views. i wont go so far as to advise you to opt from current protocol, however, maybe worth considering if this could be a factor.
You mentioned your dog was prior doing ok on one brand of raw. Maybe worth considering some other flavours or brands. I have fed brand you have but have seen willingness to eat other brands. i feed nutriment & occasionally wolf tucker....another member on here feeds Paleo Ridge. Maybe worth trying other brands as they can vary. Also worth checking with suppliers on bone content as it can vary between protein sources too.
Despite my current preferences I accept that raw is not the only feeding option. Personally I would be tempted to feed a better quality cold pressed over and above most conventional kibbles.
I might also be considering if anal glands are okay, not over fulll, impacted or infected.
Not been mentioned so I will also throw in adequate water consumption into the equation.
If sorting the issue asap is your aim I might be tempted to change a number of factors all at once, however, if your aim is to try to narrow down the issue then perhaps consider changing one or two factors at a time.
Finally you don't mention exercise & mental stimulation amounts. I am not suggesting your dog needs more of either but these factors maybe worth considering.....particularly if you feel your dog is perhaps depressed &/or sulking.
I have no idea as to what your regime &/or house environment & (dog), house rules are...maybe worth looking closely at this as one small issue mights just be a factor
Very aware I have mentioned a number of things to possibly consider......Very keen not to appear to be criticise or worry you so please take my comments as intended.....(simply various things to consider or rule out with view to moving forwards.