Once the PEP enzyme producing bacteria are erradicated from normal health mouth flora, gluten no longer gets broken apart enough to induce an immune tolerance. Anti-bacterial mouthwash may be unhealthy and same for anti-biotics due to disruption of normal oral microbiome (don’t worry i still use mouthwash lol).

Gluten degradation is absent without PEP so these shortened peptides that train the immune system to tolerate gluten are lost

New Paper: Microbiome may influence allergic response, supports your theory. Maybe the bacteria are modifying the allergenic proteins?

https://www.sciencedirect.com/science/article/pii/S096399692300385X