i have so many of these too
I think its just from the times i was sun burned in the past. these are areas of the skin with no pigment. dead melonite cells. Nothing to worry about. It doesn't really ruin the aesthetics of a tan at all imo. I think it looks pretty darn nice. adds character to the skin and contrasts the tan really well.
where i had consistent scabs and physical skin damage from deadlifting with a barbell on my shins the entire summer, I have an extremely white patch too. its the same color as these spots.
here is a pic or two of my arms. lightings awful and it seems red but it not irl.
arms2.jpg
arms1.jpg
Also, be advised that I was outside almost every single day from morning to evening this summer and spring till now here in Britain. I work outside a lot so I have been getting a lot exposure, and i did not wear suncream for this duration. I would not say it was consistent 8 hour blasts at all, but when it was sunny i was getting a good few hours of it in chunks.