After copy-pasting links with internal attachments in the Rich Text Editor (RTE), changing the label for them using the Edit link option doesn't work as the new label is not applied. Here internal attachments refer to the attachments that exist within your Jive Community.
This issue was identified as a bug and resolved in Jive Cloud release 3006.8 with the issue key JVCLD-36503 (release notes on Worx). While the Cloud upgrades are automatically deployed, if you haven't yet been upgraded or have chosen to stay on an earlier version and now would like to upgrade, please get in touch with your Account Manager/Executive to arrange for the upgrade.
After the upgrade, changing the label for links with the internal attachments in the RTE should work as expected.