When adding a PartyRelationship the value selected for SecurityGroupId is ignored as createPartyRelationship service expects the parameter to be named securityGroupId. The AddOtherPartyRelationship form incorrectly names the field groupId causing the value to be missed in the set-nonpk-fields call in applications/party/script/org/ofbiz/party/party/PartyServices.xml at line 821.
This bug can be traced back 7 years and 1 month to when the code was originally committed, showing that it never worked in the first place
1) While adding a relationship, select something in the Security Group ID select menu.
3) Webtools -> Entity Engine -> PartyRelationship -> Find
4) Search for the PartyRelationship
5) Not that the securityGroupId field is empty even though you selected one in step 1.