Ah, OK. Thanks for telling me more.
The status of 'Killed' means that the computer or server you are running this on intentionally canceled the command, often this is because it ran out of RAM / memory. Training a classifier does take a lot of memory, so this is probably what happened.
How much memory does your computer or VM have? Could you run this command on a server or computer with more memory so that the command will be able to complete?
EDIT: I forgot to mention this! If you are ok with using an older version of UNITE and Qiime2, then you could use the pretrained UNITE v8.0 classifiers. This way you can avoid this fit-classifier-naive-bayes step that requires so much RAM, and move on to the classifying your ASVs! Let me know if you would like to try that.