HI @supratim320
It's difficult to me to figure out what's going on.
I understand that you use a JS to perform some changes on a JST. It fails, but there is no visible workflow log, and the workflow restart (is it a consecutive restart, in a "warning" log (yellow icon) ? it could be an exceeded timeout)
Can you access to the supervision of your plateforme, and get the wkf process logs ? Go to the Welcome/Home button in the left upper corner => Monitoring => Wait for the details loading, then in the process list, try to open the wfserver@yourinstncename details, you should open the log journal (you have to be admin of your instance). I'm not sure you'll get more details, but it's a start.
Cedric