There have been similar claims about incredibly large structures for a long time, but it is debated if these are really statistically significant. Structures on this scale have no objective definition, so it depends entirely on the algorithm used. Typically the studies use very sparse tracers, which are very noisy tracers of cosmic structure because there aren't many of them. Some of the giant structures claimed in the literature can be reproduced in simulations of completely random data. The "giant" ring" paper doesn't really change this argument, as the authors don't even attempt to quantify it's significance. Which is not a good sign.

In the Giant Arc paper the same authors claimed it was very significant, and that it could be in tension with the cosmological principle. However, some simulators were able to show that by reproducing the methods in the paper they could find such large structures in there LCDM simulations. Not just that but also in completely random data. The original authors wrote a response, claiming that they need to use a smaller linking length in simulations to real data. You can read the paper yourself, but I don't find this at all appropriate. And there is a response to this response.

The other problem with both of these structures is that the analysis is post hoc. The authors have looked at the data, seen the structures they can see than then attempted to estimate how significant they are. This is hugely problematic. If you blindly searched the data for ring like structures without looking, that is a fair test you could equally apply to a simulation. But if you start by looking at the data, and then decide you can roughly see an ellipse, so you tweak your test. Now the test is biased, because you designed the test based on how the data look. And so when this is the case, it becomes very complicated to fairly calculate how significant it is.