Snuffles is often used as a “catch-all” term that describes the symptoms. Did the vet confirm this was pasteurella? Or is it some other type of bacteria? How were his teeth checked? Did you have x-rays done? There are a few different possibilities here. He could have chronic pasteurellosis. He could have a really stubborn URI. Or he could have another problem, like tooth roots invading the sinus cavity.
If he has pasteurella, you may want to consider trying a different antibiotic since there are reports of resistance developing with “traditional” treatments. Azithromycin is sometimes used for stubborn infections in rabbits. If he doesn’t improve with a different antibiotic, then he may have a chronic case. Rabbits that fall into this category often have to be treated with antibiotics on and off for their entire life. Some people have found that using a nebulizer or periodically having the sinuses flushed helps with symptoms.
Tooth roots are what I have more experience with. My bunny had tooth roots growing into his sinuses. This caused chronic problems, but all we could do was treat the symptoms. Every so often, bacteria would build in his sinuses and he would have to be treated with antibiotics. Then he would be “OK” for awhile.