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Moving this to the MtoA space, because this is an mtoa issue (that's why you see "[mtoa]" in the log message).
Do you have the Bifrost plugin installed?
bifrost_polymesh is implemented by bifrost_procedural_0_1.dll
00:00:00 770MB | loading plugin: C:/Program Files/Autodesk/bifrost/1.5.0/Arnold-5.0.0.0/bin/bifrost_procedural_0_1.dll ... 00:00:00 770MB | loaded 5 plugins from 1 lib(s) in 0:00.00