If a varbind in a notification payload includes
a DisplayString (or other printable string value)
containing the NUL character, then any varbinds
following this are not logged. The trap output
is truncated at this NUL character.
See the thread
Truncation of trap by snmptrapd with
DisplayString ending in null
on the -users list, 16 Sept ff
Fixed via commit 7f05daa8e0e0f533b0f12a3e1cf07641519909d6 on the 5.4, 5.5, 5.6, 5.7 and master branches.