What is the current status or resolution of Greisen–Zatsepin–Kuzmin (GZK) cosmic-ray paradox?

The Greisen–Zatsepin–Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy.

A number of observations have been made by the largest cosmic-ray experiments that appeared to show cosmic rays with energies above this limit (called extreme-energy cosmic rays, or EECRs). The observation of these particles was the so-called

GZK paradox or cosmic-ray paradox.. It was considered to be an open problem in physics.

These observations appear to contradict the predictions of special relativity and particle physics as they are presently understood. However, there are a number of possible explanations for these observations that may resolve this inconsistency.

Some possible old resolutions:

• The observed EECR particles can be heavier nuclei instead of protons.

• The cosmic rays could have local sources within the GZK horizon (although it is unclear what these sources could be). Mirror matter?

• The observations could be due to an instrument error or an incorrect interpretation of the experiment, especially wrong energy assignment.

Question: What is the current status or resolution of Greisen–Zatsepin–Kuzmin cosmic-ray paradox?