Since I set up JFrog Artifactory on our server, I have been alone in using my account (which is separate from admin account) to deploy to a library in libs-release-local, and everything works fine.
Yesterday, I setup an account for my colleague to work with, giving them the same configuration as my own account, which is simply being member of a group that can contribute to _everything. This group has Delete/Overwrite, Deploy/Cache, Annotate and Read access to libs-release-local.
We are using gradlew to build and release our lib. When using their username/encrypted password to download the artifacts or deploy a version, our server directly returns a 401 response to GET|/api/system/version|HTTP/1.1|. Keeping on the same computer, if we just switch to my credentials in the gradle.properties file, I can login successfully.
We have tried changing their password a few times, each time taking the new encrypted one to try, but the result stays the same. Of course, they can also successfully login to the webapp. We have run out of ideas on what could be incorrect in our configuration.
The issue resolved itself this morning after yet another password change. I suspect Artifactory doesn't like certain special characters, although I have no proof.
I will use this "answer" to close the question, but I'll accept any answer that confirms my suspicion or suggests to the actual cause or the problem.