Do Shoes Lose Stiffness

On my gravel bikes over the past 5-7 years I’ve used spd pedals and Specialized mtb shoes (same pair). Never had any issues. At the start of this year I’ve been getting more foot and ankle soreness when on the gravel bike (which is not there when riding the road bike indoors or outside). I’m thinking it’s unrelated to the shoes, and more like the feet getting used to steeper climbs and the pressure I put on the pedals when climbing. But is there a chance the shoes have lost stiffness? The sole of the shoe seems fine (doesn’t easily flex). Thx