I had the same problem, but it's resolved now.
I contacted twonky support via email@example.com
According to them, it's a Known issue. They promptly provided a beta version that works perfectly.
You should tell them the version of the package you are using and they will send you the link to download.
I have a QNAP T212, firmware 4.2.3.
I was using package TwonkyServerEU_8.4_arm-x19.qpkg so I was provided with TwonkyServerEU_8.4-beta-4_arm-x19.qpkg.
It works fine after 2 reboots.