[cempaka]

I thought the issue was not Unsafe methods (which are only just now starting to be marked for removal) but rather various bytecode weaving libraries like javassist. As the JDKs progressively enforce bytecode verification more strictly these libraries sometimes run afoul of the new restrictions. (I speak from a little experience here, managed a somewhat involved upgrade path from 7 to 8 way back in the day which had this issue.)

[vips7L]

I haven’t ever seen this mentioned. The real culprit was libraries that go into jdk internals when they shouldn’t have so end user applications couldn’t upgrade until those libraries upgraded.

[chungy]

That's probably another factor, and these two aren't the only ones.