Custom Fields labels are being displayed as strings after update

After performing an Update of the Xray plugin from an earlier version to 3.4.0 (like from 3.3.7 or 3.3.8, p.e.), the labels of the custom fields become displayed as a string - check the following screenshot:

This problem partially occurs if the plugin with the 3.4.0 version is installed when there are no previous Xray installations - in that case, only the following text portions are displayed as strings:

This problem is related it this JIRA 8.2.x reported bug: JRASERVER-69388