https://updates.jenkins.io/current/updates/ seems to be last updated on 18 April. 

For me this causes issues with Packer plugin - I cannot install latest 1.4.1 version. Looking at current list I see it is outdated (latest version is 1.4.0): https://updates.jenkins.io/current/updates/biz.neustar.jenkins.plugins.packer.PackerInstaller.json

Running crawler (https://github.com/jenkins-infra/crawler/blob/master/packer.groovy) manually generates a proper list:

{"list": [
{{ {}}
{{ "id": "1.4.1-darwin-386",}}
{{ "name": "Packer 1.4.1 darwin (386)",}}
{{ "url": "https://releases.hashicorp.com/packer/1.4.1/packer_1.4.1_darwin_386.zip"}}
{{ },}}
{{ {}}
{{ "id": "1.4.1-darwin-amd64",}}
{{ "name": "Packer 1.4.1 darwin (amd64)",}}
{{ "url": "https://releases.hashicorp.com/packer/1.4.1/packer_1.4.1_darwin_amd64.zip"}}
{{ }, ...}}