Changes to SD card do not persist after unmounting
This crops up a lot.
Super User has a boiler-plate QA on it - What can I do if my USB flash drive is write-protected or read-only? - but you are likely seeing the result of the firmware going into write-protect mode. 

The added confusion that it appears to accept data is a known side-effect. As they're readable, first get all your data off, then test with the Fight Flash Fraud app F3X &amp; also check formatting in another computer; but be prepared to have to trash them. 

If the firmware lock has triggered, they're done for.