Could be a lot of things or nothing. I have had a hen that occasionally sneezes all her life, but I mean like a few times a week I would hear it.
Now, I have introduced new birds that brought chronic respiratory disease (mycoplasma gallisepticum) into my flock...that makes a lot of sneezing that can also have a bubbly eye appearance and decrease egg production.
BUT, there are many respiratory diseases out there that cause sneezing/coughing. Infectious bronchitis and newcastle disease can cause sneezing too so do so research on those diseases if you see a lot of sneezing and it seems to spread to others in the flock.
I hope it is nothing but a dusty coop for you!