The default tolerances used for symmetry determination are slightly different between the default in, e.g., pymatgen (0.01), and the software we use to publish data in the Materials Project (0.1):
from mp_api.client import MPRester
with MPRester() as mpr:
summary_doc = mpr.materials.summary.search(material_ids=["mp-1271793"])[0]
print(summary_doc.symmetry.symbol)
>>> 'R-3m'
print(summary_doc.get_space_group_info())
>>> ('C2/m', 12)
print(summary_doc.get_space_group_info(symprec=0.1))
>>> ('R-3m', 166)
Symmetry determination isn’t perfect and this situation is unfortunately common