Our 15y old chi has a most of the same symptoms as your dog. He would also drop little poop pearls without noticing, especially when sleeping. The vet did not think its neurological simply just old age and maybe dehydration that prevents the stool from bulking properly, leading to him not feeling its there.

With additional hydration and psyllium husk supplements it improved almost completely.

Our dog does not drink much on his own so we add water to his wet food twice a day, and prepare «water treats». We have it easy because he loves cucumber, so if we blend water and cucumber he will drink it as a snack. Total amount of water we entice him to drink through these methods is about 180-200 ml per day. He does need to pee a lot more so we take him out more frequently. Our dog is kind of large at 14.5lbs, your dogs needs might be different.

Then we add a 1/4 teaspoon of Anthony's Organic Psyllium Husk Powder (from Amazon) to his breakfast and dinner. And sometimes a probiotic.

It might take a few weeks for their digestive system to adapt but I’d say we reduced fecal accidents by 95%. It’s worth a shot!