Version 1.4.0 of this plugin:
Repeating Group Slider & Carousel
introduces a breaking change, albeit a small one and it took me far too long to troubleshoot.
In short, the Content > HTML ID field in the Swiper element now needs the element ID without the # symbol. Previous versions all required this in order to work properly.
This is just a heads up to those who also update, as I was not able to find it discussed here, but also an ask from Zeroqode to be more transparent about when these kinds of updates happen.
Cheers!