I reproduced the problem by uncommenting this test. It's a bit strange because there are other host function tests that work fine. I suspect there is something going on with the interaction of this specific plugin and Java here but I have yet to narrow down what the problem is.
There is a JNI level problem when running the host function example that uses the kv-store. It seems we forgot to uncomment this test and get it to work: https://github.com/extism/java-sdk/blob/main/src/test/java/org/extism/sdk/PluginTests.java#L56
I reproduced the problem by uncommenting this test. It's a bit strange because there are other host function tests that work fine. I suspect there is something going on with the interaction of this specific plugin and Java here but I have yet to narrow down what the problem is.