Not all numbers displayed

From time to time some telephone numbers are missing in the address book list. If I restart once or even twice they are back.
I guess the missing ones are saved on SD card.

Why is that?
How can I prevent that?

Which version of Fairphone OS are you at? I think the SD card issues should be resolved with 1.8 (you might need to wait a bit longer for the revised update).

I got an update in December - so I think I should have this one.

Do you mean the SIM card? Then this could be interesting for you:

Oh - of course I wanted to write SIM card, sorry.