I experienced a sore tongue- and realised it had to do with the nic strength, at least from my experience. I do suffer from dry tongue from time to time, but ever since I had my spell with loss of taste- I've been very careful to stay hydrated whilst
vaping. Ever since, I have not had hardly a problem with a sore tongue or dry mouth. I've tried the various forms of Biotene, and they offer temporary relief. I found it most effective to use at night just before bed. Maybe try to lower the nic in your juice, that may help. But I think the bottom line is to keep sipping water or some sort of liquid during vaping.
I also noticed that when I first started vaping and making the transition from analogs to vaping, I had some sore tongue issues as my body was adjusting to the change.