Hi Yeny,
There should be more details about the cause of the issue in the jsrvr.log and stdlog.X under NX_ROOT\log folder. Also, it would be helpful to use the Developer Tool (F12) and then reproduce the issue and see if any URL returns an error like 404 or something. Please provide the errors generated in the logs while reproducing the issue and the results in F12 developer tool.
Hope this helps to find the root cause..
Regards,
Pablo