TechCrunch claims that the problems started yesterday (February 10) and have continued into today.
While some users are unaffected, others have reported the reappearance of thousands of old items as new posts, along with entire feeds returning that the user had previously cancelled.
The problems are making it much harder for people to use Google Reader as they cannot tell which items are new or old, particularly as the problems also appear to be affecting the timestamps.
Writing on the Google support forums, a Googler said of the problems: "The Google Reader team has been notified and someone will be looking into this."
While Google has recently focused more resources on developing social network Google+, Google Reader remains one of the most popular RSS feed-reading services on the internet. It also powers third-party reading apps, such as Flipboard and Reeder.