This is normal for the X-T2, after about 8 to 10 seconds of no use the refresh rate will drop way down to conserve battery power. If you half press the shutter it will go back to full refresh rate. Also, I believe if you use boost mode it will not do this(Or it at least greatly lengthens the time at which it goes into power saving mode.
Here is a video describing it.
Thanks for posting this, this is the exact subject matter for 90% of my photography, so very relevant for me.
I am strongly considering the X-T2, just waiting for t to get out and see some real results.