Sightly exception after migrating fom 6.2 to 6.4.2




I am facing an intermittent issue after migrating form 6.2 to 6.4.2  and this is only on single publisher,sometime on pub1, sometime on pub2 or 3 or 4(at least any of them is affected) and restarting that publisher resolve the problem. i am trying to understand the pattern but till now no luck.

here is the screenshot:


I am using aem 6.4 sp2 and uber jar is also 6.4.2

sometime restating (Apache Sling Scripting HTL Engineorg.apache.sling.scripting.sightly) bundle also helps.but i  am looking for a permanent solution or any pointer 

Thanks in advance.