When we release a new engine, it is not deployed to all on-premise customers at once, but gradually over the course of a few weeks.
26 September - 10 October 2017 is the timeframe during which 6.9/55.990001702 is being deployed.
If you do nothing, you can expect the new engine to be deployed to your TEX appliance in the next week or so.
You can also do a manual update by using the steps in the following SK: Offline updates for Threat Emulation images and engine
As for why the js is not detected on your on-premise appliance, we make continual improvements to catch malware and reduce false positives.
It's possible something in the 6.9 catches it, whereas the 6.8.2 engine did not.
If you see a difference after getting the 6.9 engine on your local TEX appliance, I recommend opening a support ticket.
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