Liz Buchanan BVSc MRCVS
Keymaster
Common reasons for mouth-breathing, include stress, (goes away again when no longer sressed), pain or heart / breathing problems. If this has not resolved it sounds as though you need to present to the vet again, possibly as a matter of relative urgency. If you go again and they don't seem concerned, it would be a good idea to ask at what point / severity it is important to be seen, or else why they think you might have been seeing the sign (what the possibilities might have been) and how to go about ruling out some of the more severe possibilities. I hope that helps a little.
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