I just ran into this problem myself and found a temporary solution so I wanted to share my experience with the rest of the community.
I have a Fairphone 3, after setting it up and restoring my data from a Google Drive backup I added a 128GB SanDisk Ultra micro-SD and formatted it as internal storage. I did not migrate my data at the time because I needed to use the phone right away and the procedure is rather long.
Fast forward one year the photo app informed me that I was running out of storage so I plugged my FP3 into the charger and started the migration procedure to move data to the SD card. The procedure finished successfully and the settings app showed the correct amount of data on both the onboard storage and SD card.
That’s when the trouble began: the photo app would take pictures but refused to save them and WhatsApp refused to download any kind of media (audio, video, PDF files, etc…).
I did not want to reformat my phone so I tried the following:
- From the storage settings I ejected the SD card
- I shut down my phone and physically removed the SD card
- I rebooted my phone without the SD card, it complained that it was missing
- I shut down my phone again and re-inserted the SD card
- I rebooted the phone again and it picked up the SD card. Now the photo app works correctly and WhatsApp is also working as excepted
I’d like to consider the issue fixed by this little roundabout but I’m not sure if it really is: the storage settings don’t show the same amount of storage in use compared to when I did the migration. Additionally it shows that all the storage used on the SD card is taken by apps, but that’s not the case, the vast majority of it should be pictures and videos, but the corresponding entries show as if none of them were stored on the card.
I have extensive experience in Android development so I can help debug this issue. If Fairphone’s developers would like to contact me directly I’d be glad to help.