Android SD Card Swap

A couple of weeks back my phone (FairPhone 3) started showing 'failed to save' errors for apps which used the sd-card, things like the Camera and Obsidian. It would just say 'Failed to save', no more information than that, great, thanks 😡 A device reboot would get it working again. What is this, Windows??? I'd recently-ish installed Shelter, and for no good reason I'd assumed that it was…