Could it be because of the LN testing?
Not likely. This is probably due to Segwit starting to be rolled out more and more.
LN is still a giant experiment at the moment, and I can't really recommend getting involved with it right now, unless you are into masochism.
We'll see how much of a difference LN starts to make once they hit 0.6 (0.5.2 right now)
We have less tx per day comparing to the previous weeks. *Maybe* that's a good explanation after all.