@Hoots and @magoo
First of all welcome to the forum; and great, that you did not give up on Fairphone.
Hopefully this SD-card trouble is and remains your only concern.
Since there are quite a few different SanDisk cards out there, it could be helpful, to be more precise on the model. (The more info, the better; I would guess.)
If you take a look at the thread on compatible microSD-cards for the FP2, you will find, that e.g. the Samsung PRO+ 128 GB was reported to cause problems, while the Samsung EVO+ 128 GB and the Samsung EVO 128 GB were reported to work fine.