Project migrated from 5.6 to 5.7 - transparency breaks

Development Rendering
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I migrated a project from 5.6 to 5.7. All my materials work fine except for glass. Even when I create a new substrate translucent material from scratch, there is no distortion from either the IOR or normal maps. I see a sort of reflection change from normal maps, but thats it. What project settings would be messed up, or need changing, during migration?

Many thanks in advance

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image1895×877 177 KB
actually, this problem is happening in a brand new project. What have I missed. This material setup worked fine in 5.6.