Apple's support forums are awash with users complaining the iPhone 4S suffers from poor performance when upgraded to iOS 8, with many users warning that the software slowed their devices when compared with iOS 7.
Other problems noted with the upgrade included software instability, battery drain and increased handset temperature.
Forum user The Fersh warned iPhone 4S owners to avoid iOS 8: "Don't upgrade to iOS 8 if you have an iPhone 4S, it's unstable on this model, drains your battery and the temperature inside goes up!"
Fellow poster Rsohailr went on to detail more problems encountered with the 4S: "Could not open Safari, phone hangs up. Have to reboot again and again."
These comments extended beyond the forums and onto Twitter, where frustrated owners of the older iPhone vented their frustration.
Such problems are perhaps not surprising given that the iPhone 4S is more than three years old. While the iPhone 5S and new iPhone 6 models feature 64-bit architecture in their processors, the iPhone 4S has to make do with an older, slower dual-core processor.
However, some posts on Apple forums also highlighted problems with more recent iPhones when upgrading to the new iOS version.
This issues range from temperamental Bluetooth and wireless connections, to crashing cameras, mangled music and scrambled syncing on iPhone 5 models and above.
V3 noted that problems, questions and complaints about iOS 8 were cropping up on forums every few minutes, highlighting that the OS might not be as polished as expected.
We contacted Apple for further comment, but the company has yet to respond.
Sales of the new iPhone models have not been dented by concerns of bugs in iOS 8. More than 10 million new iPhone 6 and iPhone Plus handsets were sold in the opening weekend, making the iPhone 6 models the biggest-selling iPhones of all time.
