"Call to a member function getPHID() on a non-object" while creating milestone using conduit

Version information:
Using the stable branch

phabricator c4b4a53cad7722f031b725f8b41511e9d341d033 (Fri, Dec 13) (branched from 54bcbdaba94a3573e128c6498816dbfa41d3a9cb on origin) 
arcanist cc850163f30c4697e925df0d6212469679600a2c (Tue, Nov 19) 
phutil 39ed96cd818aae761ec92613a9ba0800824d0ab0 (Sep 30 2019) 

Reproduction steps

1 - Create a Project via UI normally
2 - Use project.search to find project PHID
3 - Send request data to project.edit to create milestone referencing the project PHID
4 - See error message

Sample request using curl:

curl http://phabricator-instance.com/api/project.edit \
    -d api.token=api-lca6qpfpngkpgsrsrkppzuqaivjj \
    -d transactions[0][type]=milestone \
    -d transactions[0][value]=PHID-PROJ-rt4ibxhpq3wc7gk3xyvv \
    -d transactions[1][type]=name \
    -d transactions[1][value]=test_milestone

I tested using a test instance, but the error did not occur, I suspect it might me something related to this Differential review https://secure.phabricator.com/D20920

My test instance: https://test-gukp62gxu4nd.phacility.com

This used to work but some time ago it stopped working, and only now I noticed it