Dear , all
        We found that when lava executed a script which may output a long string (more than 30000 bytes) in a line (only one line break), lava web UI always hung and there was no more lava log outputting and devices under test (short for DUT) were still powered until Lava Job time-out function triggered , however, after checked the whole log file  we found that cases behind the hanging case were executed (there's new files generated) .
       So the problem is that when lava encountered those cases lava web UI always hangs and DUTs may not be powered off when all the cases are completed ! 
          best wishes,
 Chuan Su