vector capacity shows 0 even though it is reserved

This here

vector<uint32_t> v = test->getV();

Makes a copy. v isn't actually a reference, so even though you return one, it has to make a copy anyway. Because it is a copy, it doesn't need that same amount of reserved space. If you actually get the reference instead like this:

vector<uint32_t> &v = test->getV();

The output is 32 both times.

The copy-initialized v following vector<uint32_t> v = test->getV(); is a value copy of test->getV().

The C++ standard does not require the copying of the source vector's capacity following copy initialization, so the capacity of v is allowed to be any value subject to it being greater than or equal to the number of elements.