That's Broad mites!
They are as small as the diameter of the LEG of a white fly! So, you will not "see" them by looking through a lupe.
They attack the veins of the leaf and that gives you what you see in the pics.
The SINGLE most EFFECTIVE way to get rid of them is Forbid 4F. You will play hell trying to get them with a "contact" killer. Forbid is not technically a poison but an acid that blocks lipid fat use by the bugs internals. This makes them "dry out" and die. It works on all stages of the mites growth. Simply a light spray on the tops of the leaves is enough.
You can find this in affordable amounts on ebay.
I'll bet my whole grow it is NOT TMV or Sunn-Hemp MV!
In all my time growing, myself and others in our little "collective" have sent HUNDREDS of samples to MSU for testing and NONE have come back as positive for MV,,,PERIOD ! (they did find broad mites)
Some info on MV above has been left out. It is HIGHLY contagious and is spread by contact with the plant alone! If you touch an infected plant and touch one that's not,,,,bingo, you passed it on. It can be transmitted by bugs touching and flying to the next plant. Even buy plants touching plants as the wind stirs them.
BTW, Sunn Hemp is a BEAN and not a member of the Cannabis family.
This info is all derived from talking with Professors of agronomy from MSU (GO SPARTANS!).
I wish I had a dollar for every time I give info on TMV/Sunn-Hemp, high P in flower, Forbid, and pH in soil.
P.S. Oh yeah, MV DOES effect the yield of any infected plant that does get it! By a lot!