STABLE version -- 5.1.1130.129

[tamer]

yes the flag helped, but how stable is work with this flag? the flag was disabled
it's time to update the engine version anyway

Never had any issues caused by this flag, it just enables the newest js features that would be available in the next few releases. I would even make it enabled by default on cent.
I think it would take some time to update. There were many unpleasant changes recently. And the latest stable v130 had some nasty bugs, ex. the Fetch with Promise caused 10-15 requests per query and some other bugs.