How can I recover missing iCloud storage space?
I ended up phoning up iCloud support, and they were similarly baffled. They tried a load of things (none of which worked), and eventually they then asked me to delete the WhatsApp Documents &amp; Data storage. Despite it saying that only 350MB was being used by WhatsApp, deleting this immediately freed up around 2.8GB (350MB plus the ~2.5GB of "lost" space) in iCloud.