[pilif]

due to the modularization effort that went into Java 9, a lot of previously accidentally exposed internals have become inaccessible.

Unfortunately, many widely used libraries depended on said exposed internals and now stopped working.

Many libraries have since been updated, but often in form of new major releases and not all libraries give the same backwards compatibility guarantees as Java itself does.

So even if you yourself were a good citizen, relied only on public interfaces and got rid of uses of deprecated API in a timely fashion, then some libraries you depend on might not have done so or might have changed a lot since you last updated them.