If the SD cards were heavily uses the might be worn out.  Did you try to factory reset the a69?

The sd cards that didn't work this time were always working before. No,my camera didn't get wet,I regularly last used it less than a month ago in perfect weather conditions. It worked fine. Any other ideas?

Welcome here. Don‘t swap SD cards between cameras without formatting. And keep in mind that your camera is quite old so cards with bigger capacities might not work. Concerning the a69 - did the camera possiböy get wet?