I have never had this error on Linux and this is running FreeBSD as root:
Wed Aug 9 04:29:34 2017 us=329050 Cannot allocate TUN/TAP dev dynamically
Wed Aug 9 04:29:34 2017 us=329832 Exiting due to fatal error
The Solution
You need a kernel module that is for some reason not automatically loaded like Linux:
kldload if_tap
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