Hi there and thanks for your question. Sorry to hear that Lynus is not feeling 100%
The most common reason for scooting is indeed a problem with the anal glands. If a dog is still scooting after I have expressed anal glands then often I consider whether there is an infection in the glands. Also, some dogs have anal glands that are very difficult to express. While some groomers can do an excellent job at expressing anals many will express them externally rather than internally and may not empty them completely.
It does, unfortunately sound like your boy needs a vet visit to have his anals thoroughly examined to see if they are indeed fully emptied or if there is infection present.
Another possible reason for this behaviour is if there is an infection or allergy that is irritating the skin of the anus. You should be able to tell if his anus is inflamed, but then again, if you haven't looked at many dog anuses it may not be that obvious! If your vet thinks there is an infection, wound, or allergy they will prescribe antibiotics and possibly some steroids.
You may want to try adding some fibre to his food to help to loosen his stools. You can do this by adding 1 tbps of pumpkin to his food twice daily or a pinch of bran to each meal.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.