I have my project files under ~/SquareLine/(sll.slp.spj)
When i click on import, the preview is shown, but if i open the project its empty 
Hi, to investigate the issue further, we need the log file, which you can find here: Troubleshooting | SquareLine Studio
Please send it to us so we can identify the root cause. In the meantime, you could try removing special characters (such as parentheses) from the image filenames, as that might be causing the problem.