The same thing happens to my mostly husky mix, Mylo about 2-3 times a year, EXCEPT he does not get any scabs. He totally blows his coat, his fur gets very thin & coarse almost wirery. He also seems to get skinnier. This has been happening since we got him @ 4 months of age it has been 6 years now. He also was itching a lot. We took him to quite a few different vets & specialists, got allergy tests & many different bloodwork tests done on him. We found absolutely nothing wrong w/ him, thousands of dollars later. We have tried different foods, supplements, medicines & nothing works. He has always acted like his normal self & had no other symptoms. Every vet & specialist we went to after finding nothing wrong said that it just must be his own way of shedding. It has been know for dogs to shed like this although it is not too common but it does happen, so that is the conclusion we setled on.
Maybe Nebo also just sheds like that although I am not sure about the scabs? Maybe from insects or just from itching? Maybe he did get something from another dog at srtut your mutt?
The fur in your pic looks just like Mylo's fur when he blows his coat. Some people think I shaved him in some areas & is starting to grow back, like a reverse mohawk.