GPG error signatures couldn't be verified because the public key is not available

Hello, I don't know if this can be related to #4248 (closed) as it's very old issue, but this one recently came up. Any changes has happened?

Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease                   
Hit:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease           
Hit:4 http://archive.ubuntu.com/ubuntu bionic-backports InRelease             
Hit:5 http://archive.ubuntu.com/ubuntu bionic-security InRelease         
Get:2 https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease [23.3 kB]
Err:2 https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
Fetched 23.3 kB in 3s (7,244 B/s)
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
W: Failed to fetch https://packages.gitlab.com/gitlab/gitlab-ee/ubuntu/dists/bionic/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F
W: Some index files failed to download. They have been ignored, or old ones used instead.