Neo4j 3.5.x: It is not allowed to define functions in the root namespace

So, just upgrading from 3.4.x to 3.5.6. I had to rebuild our plugin, as it depends newer versions of other plugins. No other changes. Yet, I am getting the odd error:

It is not allowed to define functions in the root namespace please use a namespace, e.g. `@UserFunction("org.example.com.randomUUID")

I've tried using increasingly lengthy names, e.g.

@Procedure(value = "com.company.project.category.function", mode = WRITE)

But the error persists. I feel like I must be missing something obvious, as I can't find any references to this issue. Little more background: our plugin defines nine @Procedures and no @UserFunctions, and defines a transaction handler. It's presently a mix of Kotlin and Java code (not that it would seem to matter).

Thanks!

Seems to be related to dependence on tx-apitracking here.