I took a look at the test bench, and the Unlambda interpreter used supports like a third of unlambda, not including input. Since 79/80 of the tests require input, it isn't really possible to solve them. The best anything did on them was 1.2%, which is 1 test.
I reported it https://github.com/Lossfunk/EsolangBench/issues/1 but haven't heard back yet