I have had similar kinds of sensations and even went through a very frightening "twitch" in my face and mouth during a very intensive over an hour long meditation.
In my experience, not only does it subside in time, but as these channels open (and that is what I have found these kinds of things to be, in my case), I have found much greater levels of healing.
I do not believe it is anything to worry about, and on the contrary, I think it is a good sign. However, if you are concerned, the place to ask, is not here or even Master Lin, but a health care practitioner.
When you ask has Master Lin, "guaranteed the safety of SFQ?", I am not sure exactly what you mean or are asking. Why would Master Lin spread SFQ and stake his reputation on this if he did not think it was not only safe, but helpful? Can he absolutely guarantee that nobody will ever have adverse reactions? That is impossible with pretty much any practice or exercise.
I can tell you, in my humble opinion, as a somewhat advanced (or at least "advanced intermediate"
) Tai Chi Chuan and qigong practitioner of over 35 years and now a certified teacher in two forms of qigong, including SFQ Level I, I believe that SFQ is safe.
For more information about adverse cyclic qi, I think you will have to check a different system that reports more incidents of this syndrome. Does not seem to happen much, if at all with SFQ.
In summary, I would let go of the fear and concern and just chalk this up to progress.
Hope that helps.