I have found a problem with Hyperlinks in the description of custom fields. I have created the hyperlink using the "External link" option and it is created as before. However, then the hyperlink is not displayed in the description, only the text (attached screenshots).
That is available on server but not on cloud. The functionality to display HTML content was removed from Jira due to security reasons, so currently it's not possible to add a clickable link on field's description because this field does not have a Wiki Markup renderer.
There is a feature request suggesting the implementation of such ability:
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