Of course, 20dB difference is not "normal", so you need to look for mistakes.
It looks like your dimensions do not match, there is some overlap (pin position conflict) in the top left feed.
And several nodes show that nothing is connected.
View attachment 167303
What did you compare, the schematic with microstrip models to the Momentum result of the same layout?
One possible mistake with Momentum (not related to bend) is the port width, at positions where the device terminal width is very different from the edge of the line where the port is placed.
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