Hi there,
I’m new to the forum. I have a similar issue with the SD card(s) in my new Fairphone 4, which I’ve had for about three weeks now. Since the suggested solution did not work for me, I wanted to post here showing my problem.
I keep music on my SD card which the FP doesn’t correctly recognise and the music player app (Pulsar) does not play. Not all files appear in the file explorer, and the bit that is there can’t be played. Checking the music files on the computer, everything is there and can be played.
Pictures and videos taken with the FP camera saved on the SD card started being damaged while saving or disappearing altogether two days ago, without me being able to recover them via computer.
I’ve tried an old and another freshly bought SD card (bc I first thought the old card is broken; both are by SanDisk, the same as OP - has someone tried with another manufacturer’s model? I don’t have any at hand rn), always formatting as portable storage, tried several times formatting and reformatting on the computer and inside the FP and nothing worked.
Also getting random notifications “issue with SD card - tap to fix” which prompts the FP set-up. Following the set-up and then trying to put the music there does not help.
Sometimes the system shows “ejecting SD card - don’t remove” and when I press “manage” I can’t really do anything. These notifications disappear after a restart, but show up again after 1-3 days.
However, I think I found out that the FP formatting seems to not work properly on my device. When being prompted to fix the SD card issue or for initial set-up and formatting the SD card as portable storage (which should erase all data anyway), the FP file explorer shows the card is clean afterwards, but when I put it into the computer, all files are there and the music can be played, which means to me the formatting did not work. This happened every time I tried, not only once.
I also tried this thread’s solution by formatting at the computer first and then formatting on another phone (in my case, a Samsung Galaxy Note 10) and skipping the FP set-up, which didn’t help either.
So I’m here posting to ask if anyone has got other ideas (apart from a factory reset, see below). My other ideas would be it’s an issue with the SD card slot or a compatibility problem related to the manufacturer (SanDisk), but I can’t test this rn. Has anyone got other experiences related to this?
(Side note: In the music player app Pulsar there appears a java language script error message, the media format may not be supported. I tried with the original MP4 and M4A files mixed and with everything converted to MP3, both doesn’t work. The player worked fine on my old phone and YT Music on the FP works too, with the bit of music that is visible/accessible, but there is still the issue that most music in either format does not appear in the file explorer on the phone. Also, independent of the music format, it’s always the same pieces that seem to be there and all the others not, and I haven’t found out what this causes.)
My Fairphone 4 is updated to the newest software/security fix, the OS is the preinstalled Android 11.
I contacted support about this and they suggested I perform a factory reset, which I treat as last possible solution bc the procedure with backing up all chats etc. takes a lot of my scarce free time and I still hope there is an easier solution.
Looking forward to hear from you and glad for any bit of help, sorry for the long post 
They are old like me, from the last century.