Are you adding anything to his kibble like omega oils?
It could well be his diet (kibble or treats). His digestive system may not be processing everything within 8 ~12 hours. So, the food he ate yesterday morning may in fact be the cause of cannonbutt the following evening. Going grain-free may be well worth a look.
Also, parasites are bedevilling little creatures. My oul' boy (
) had a wicked case of liver flukes which were not only difficult to diagnose but like, your guy, one day he'd be sicker than all get-out and the next he'd have normal BM's and no
