I’m not seeing any problems when I test a relationship field as a sub field of a repeater.
The JS errors you posts could indicate a couple of things. On is that there is a conflict with another script, try deactivating other plugins. The script conflict could also be in your theme. Another thing that can cause this are plugins that “defer” loading of scripts or in some other way alter the way that scripts are loaded.
If no results are being show then this can happen due to a PHP error during that AJAX request. Turn on debugging and error logging and then check for errors in the error log https://codex.wordpress.org/WP_DEBUG
