Hello,
How about adding a Fx to your link with the function translate(field, ' ', '%20') ?
You can add a rule to the repeating control. And, it should fire when the secondary data source gets loaded. Just go to the data source, select the repeating group in your data fields and add the rule there. You could simply add the rule to the link and have it replace, but be careful because it will continue firing so you'll need to set some other condition so that it only fires once.
If that doesn't work, then I would suggest you to use qRules 'encode' command. That will definitely do the trick.
Hope this helps. Thanks!
- Prachi