I have always kept Optimise Iphone Storage under iCloud for Photos on. Since last week however, it has stopped optimising and saving space locally on my phone.
One possible cause is the use of Google Photo's backup and sync function. I turned that on in Google Photos again after a long time last week in order to share an album with Android users. Google search suggests that Google photos would download the full res photos from iCloud in order to upload them. My iPhone's free space did plummet from more than 10GB free to now less than half a GB free.
Yesterday, I turned off backup and sync in Google Photo and later uninstalled the app. But Photo is still taking up 34GB of my local iphone storage. Now I have 80/200GB free on iCloud, less than 500mb free on my phone, Photo app is telling me it has stopped updating because I am low on storage.
I have kept my phone plugged in all night and on a fast wifi. The Photos storage remained at 34GB after 12 hours unfortunately.
How do I make the Photo & icloud optimisation runs again to free up my phone storage?
PS: My iCloud photo library is up to date. Yet in my iPad, my photo library is taking up less than 3GB of space. So somehow it has to be the full size download in my iphone that is taking up a whooping 30GB of space.