I was hit bug duplicity bug 1538333. Recompiling EPEL's duplicity RPM to the latest version (0.7.15) fixed it; recompilation was very simple: no patches or anything like that had to be added to the .spec file. I suggest that EPEL's duplicity be updated from version 0.7.13 to the latest duplicity version. As far as I can tell from the release notes, there should be no backwards compatibility issues when moving from v. 0.7.13 to 0.7.15. Note the following part of the release notes for 0.7.15: "Please note that a major memory hog has been fixed. This should help with almost all out of memory bugs that have been happening since 0.7.03, a long while ago." That should be another good reason for updating EPEL's duplicity version, I think.
duplicity-0.7.15-1.el7 has been submitted as an update to Fedora EPEL 7. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2017-dfbc39ae13
duplicity-0.7.15-1.el7 has been pushed to the Fedora EPEL 7 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2017-dfbc39ae13
duplicity-0.7.15-1.el7 has been pushed to the Fedora EPEL 7 stable repository. If problems still persist, please make note of it in this bug report.