Well, the no_proxy implementation is not really full featured. Here is a list of upstream RFE tickets which might be relevant:
https://bugs.ruby-lang.org/issues/8317 (this included patch, you probably want to test it if it helps)
So it seems upstream applied the patches from
as well. I requested backport to older versions as well:
Would you mind to test which of the patches resolves the issues you describe above?
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.