Maybe I can help you,we also have this problem before 2 month, and we found this is because the pretty-faces's version 3.2.0 dependency wrong, you can change seam-bom to latest version or override the version declaration:
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<dependency>
<groupId>com.ocpsoft</groupId>
<artifactId>prettyfaces-jsf2</artifactId>
<version>3.3.0</version>
</dependency>
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good luck!