Google's newly reported photo service which made its debut at Google IO this year was met with plenty of excitement for more than a few reasons, including what was probably going to gain it the most attention, unlimited free storage of all your photos. The app and service has been available to users for about a month now and all seemed to be going well, up until yesterday when users started complaining that they were being met with an unlisted data cap that wasn't supposed to exist. The reports came from multiple users claiming the same issue, that they had began a large amount of photo uploads which would end up stopping during the process. Not only were their uploads ceasing to continue, but uploads were stopping across devices.
The temporary fix for the time being seemed to be upgrading from the unlimited free storage to one of the Google Drive paid monthly options. After completing this action multiple people reported that their uploads immediately began resuming after initiating the subscription to a monthly paid option of Drive. That temporary fix seems to have turned into a permanent one as Google now states they have fixed the issue with the upload data cap, although they made no mention of what was causing people's uploads to stop in the first place. Based on yesterday's information from users, it seemed that those who were experiencing the cap were uploading varied large amounts of pictures, so it's more likely that the amount of data used to complete the uploads was more of a factor than how many pictures were actually uploaded.
Now that Google has fixed the problem, everyone should be able to resume uploading pictures without running into subsequent issues if they experienced them at all. It's doubtful that anyone who wasn't uploading a huge number would come into contact with the cap though. Now that unlimited is back to unlimited, the only other caveat Google Photos may have is the photo compression which comes into play, where pictures get compressed into a number of different formats, all the while leaving the original out of the equation. The point being, if you want to keep the original format of the pictures you're uploading and you're only using the free service, make sure to keep the original image file backed up somewhere else, or pay for a monthly Drive option.