LNK414 LED driver malfunction after polyurethane filling of housing

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Hi,
We design of LED driver based on LNK414. This LED driver should be mounted in a plastic housing and then the whole filled with polyurethane adhesives. This solution will improve the heat transfer and reduce the temperature of all components.
Unfortunately, we encountered problem with LED driver, after pouring.
a) Before the flooding of housing:
* photo 1* oscillogram no. 1result: LED driver is working properly (0.65A output current)
b) After the flooding of housing:
* photo 2* oscillogram no. 2result: LED driver incorrectly action, some abnormal current ripple (shutdown?)
The applied weight polyurethane has good thermal conductivity and very high resistivity. It is dedicated just to coat printed circuit boards... We also checked other fillers (eg silicone). The effect is the same - malfunctioning (after filling).
What is the cause?
Robert

The conductivity of  polyurethane might be higher than the air, and this higher conductivity might provide the path of switching noise getting into Vpin, Rpin, and FB pin of LNK414.

It is necessary to review the layout, which should be done as suggested in the LinkSwitch-PH data sheet.