Stopped working with last 11.2 update.
There has been a API change GetLootMethod() vs C_PartyInfo.GetLootMethod and also their function return output.

GetLootMethod()
lootmethod
string (LootMethod) - One of 'freeforall', 'roundrobin', 'master', 'group', 'needbeforegreed', 'personalloot'. Appears to be 'freeforall' if you are not grouped.

C_PartyInfo.GetLootMethod() returns integral
method
Enum.LootMethod
Value Field
0 Freeforall
1 Roundrobin
2 Masterlooter
3 Group
4 Needbeforegreed
5 Personal