Due to a typo in the method name, corCompSymm objects call the base-class's corFactor method instead of its specialized version.
At line 1411 of R/corStruct.R, the declaration
corFactor.compSymm <- ...
corFactor.corCompSymm <- ...
This bug shouldn't affect correctness, because the base-class method implements the same semantics as the derived class, but I assume the specialized method is likely more efficient.
Disclaimer: I'm new to R and wasn't able to confirm this bug or the proposed fix in a debugger. I hope maintainers who know more than me can check that my suggested fix makes sense, and apologies in advance if this is off base.