You might want to have him checked for megaesophagus which is a known problem in this breed
www.marvistavet.com/html/megaesophagus.html
He could also be intolerant of one of the ingredients in his regular food. Swapping to a minimal ingredient food like California Natural Lamb or an alternative ingredient food like Wellness rabbit, fish, venison etc might help.
Plus lab pups eat odd things and foreign non food items in the stomach or intestines can cause vomiting issues.
You need help from your vet on this one to determine the problem and the best way to handle it.
Hope this helps you!
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