I get that same issue with my wacom intuos when using Sai. I'm using Sai Version 1-2 (from the looks of the icon). I feel like it is just a communication problem between the programs that pops up on occasion. I wouldn't get a new tablet at this point since it has no issues with the other programs (telling you that it is not a tablet malfunction).
It could just be that you are running too much without knowing as well and it is freezing up the program. If you go to task manager on your computer, and then more details, it should show you how much of your CPU (Computer Processing=computer program running) you are using. Sometimes programs don't close properly and will continue running in the background taking up a lot of space, and depending on your computer, this could interrupt programs. Sai and the tablet itself run on task manager, so you can see how much that takes up compared to Gimp/Photoshop plus the tablet. I know I like to leave tons of layers in Sai, which can make it a bit worse due to making the file size larger.