White lumps in corners of mouth- has any owner ever seen this before?

Hi all, pulling my hair out with this and hoping someone might be able to shed some light. A few days ago we noticed he's got white growth / lump in the corners of his mouth (inside upper lip on the right hand side, inside lower lip on the left hand side). Took him to the vets but he wouldn't open his mouth too well as he was quite nervous. Ask the breeder if she's seen it but she's also perplexed. Anyone ever seen this before?