Why does my usually chill dog act anxious only during thunderstorms, even with all the comforts I provide?

My dog Max has always been super laid-back, but lately, every time there’s a thunderstorm, he turns into a nervous wreck. I’ve tried playing calming music, giving him his favorite blanket, and even using a snug vest, but nothing seems to fully ease him. It’s only during storms, and it’s been going on for about a month now. I feel bad because I want him to feel safe, but he ends up pacing and whining despite all my efforts.

Has anyone else noticed their pet acting out like this only in storms? What helped you calm them down when nothing else seemed to work? Is it normal for this to just suddenly start happening after years of no issues?