The name Roku 3 was applied to two different models that came out in 2013 and 2015, so they’re somewhat old devices, but still supported/updated by Roku. However, not every channel supports every old Roku device. Some but not all channel/apps have a list of supported device models on their websites. And some devices just develop problems over the years.
Of course, there are other problems that can cause streaming issues, such as Wi-Fi interference, ISP problems, overloaded servers at whatever streaming service you use…, so I can’t guarantee that replacing the device will fix everything. Are you getting specific error messages or specific behaviors on specific channels?
If you look around, you’ll see some threads where some people find that certain channel/apps seem to be a little buggy, though apparently not for everyone. For example, as I type this, there is a thread on the first page with 254 replies about problems on Paramount+. However, I have that channel and have never had issues with it. Disney+ is another one that some people have issues with.
The only thing adding an SD card can do for you is add 2 more megabytes of channel app storage space (it only uses 2 megs no matter how much larger the SD card may be). That means it can keep more channels installed at one time and make less frequent the need to swap out one that hasn't been used in a while in order to re-download the one you are trying to load. It serves no other functions.
Roku Community Streaming Expert I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X