Does "Download and Keep Original" require manual sync of each photo? Following the update to iOS 10.3.1, my phone warned me (unnecessarily as it turned out) that I had too little space to store all my photos at full resolution, and suggested that I switch to "optimized" storage (which for those unfamiliar with the feature stores a uselessly blurry simulacrum of the original only), which I foolishly did.



I immediately realized my mistake, and restored the "Download and Keep Originals" setting. But this appears to have had no effect. I still see only the placeholders, until I click on an individual photo and wait for it to download.

So the question is: what does "Download" mean? Does it mean


download all photos automatically (e.g., in the background over time) or 
download a photo only when it is viewed?


If the answer is 2, is there a way to force all my photos to sync at full resolution to my iPhone without clicking on each individual photo (which would take about a month of continuous clicking, with no breaks for sleeping)?
To downloads all photos, Download and keep originals will retrieve all images from the cloud and save them to your phone.  Optimize storage will only download when photos are viewed and/or are needed by an application.  

It may require you to plug your phone in, connect it to Wi-Fi and wait for a bit for all of the photos to download, as you said there are quite a few.  It may help to have Photos open beforehand too.

Source: Experience &amp; Apple Support documentation.