I had exactly the same issue (except formatting my system). SD card was broken, and it placed itself into read-only state for data recovery. I could delete fil

I had exactly the same issue (except formatting my system). SD card was broken, and it placed itself into read-only state for data recovery. I could delete files, but those would reappear. Formating would work until restart etc. Write cache was responsible for this weird magic. I got card replaced as part of warranty.