There are no claims of Thunderbolt support from TrueNAS. There has been no development or testing.
It probably works because the Linux kernel has some support for it. It may not work, because it has never been tested as part of a system. In general, nothing works unless it has been tested and fixed. To expect otherwise is irrational.
So, its an experiment. We generally recommend these experiments be done with developer level skills. It would be useful to get testing and proposals on how to fix the issues found.