OK, if you think it is not Adobe library, it is your right.
Xournal does not use Adobe pdf library, so if things work in it it proves it can work. Nothing more nothing less.
If pdf is viewable on PC, but not in Onyx again proves nothing concerning Onyx x Adobe bug. Even if PC uses Adobe library, it will not be the same one like on Onyx reader.
There is possibility that Onyx programmers do something wrong using Adobe pdf library, but more probable is the bug in Adobe library.