There are different degrees of "stagnation" and also different causes. Could you paste the distances from a few of the last iterations and also attach the out.xml file?

Ok, that does not look like a nightmare. Maybe working a little with the mixing history already helps. You could try the following.

1. If there are any, remove all files from the working directory that have names like "mixing_history" or similar, maybe with a suffix.
2. In the inp.xml file set calculationSetup/scfLoop/@maxIterBroyd to 10.
3. Run Fleur for another 50 iterations.

Don't forget to make a backup of the working directory before you do these steps.

The density mixer uses data from previous density mixing steps to improve the convergence behavior. But sometimes this has the opposite effect. We might have such a situation here. Then it is a good idea to remove this mixing history from time to time. Whenever fleur stops in a regular way without a fully converged density it writes out these mixing_history files that are read in when you restart Fleur. This is why we delete these files. The maxIterBroyd tells Fleur after how many iterations the mixing history is reset. So with the changes after every 10 iterations we start with a fresh mixing history. This effect will not become visible in only a few iterations. Therefore I suggest to perform 50 iterations to see whether these were beneficial changes.

Another question: After how many force relaxation steps did this occur? Was it after the 2nd step?