Interesting !
These areas are in the fat pad.
The plantar fat pad has two components.
The area right beneath there skin is the micro-chamber fat pad and this is quite firm.
See to that is the macro-chamber fat pad which is softer and important for shock absorption.
The lesions you have are in the macro-chamber fat pad.
The most common lesion we see here is an area of fat necrosis from chronic compression that leads to adventitial bursitis.
We see it most commonly in the area of the metatarsal heads as this is the highest point of compression.
So this is a possibility.
Other than that, any other cause of inflammation or infection within the macro-chamber fat pad should be considered.
Your images are consistent with adventitial bursitis or any form of inflammation / infection within the macro-chamber fat pad.
Steve.