You have to be in first person view to avoid this message "You try to cast", it cappens because your camera angle updates only while you move in third person mode, while in first person mode its angle updates on camera rotate. So actually in third person view it can looks like you facing forward, but actually its not and on server side you facing back, and that why you get this messay "You try to cast ... fail". And your armour bonus -15% or -30% means that offencive spell fails by this % so even if you facing right direction with -30% bonus means 1 of 3 spells migh be failed, 30% actually alot and can happen many times in row, but this is not the case on the video, there is rather camera angle issue.
Since I'ts imposibble to get logs of true power casts, I'll reffer to skillgain chance which indirectly indicates power.
Also about power. I can defenetly tell you that some skills like Botd, Litd, Wa have differend difficulty according to skillgain chance I count for long period of time. For litd its 34% with my channeling, for botd it 41%, I had many of such weird situations that looks weird for WO, with WU mech knowlage.
And yes, some time you enter the game and your skillgain chance for hour period of time maybe crazy low or crazy high, but if you cast for longer it always brings to normal and fits to grinder skillain chance calculation.
We can build skillgain chance graph by count casts we done and skillgain we got for same period of time, which info available in log files. So generally your skillain grapgh can look like this (screenshots below). And you can see there huge spikes, platos, and huge drops - it means your power sometime very lucky and that why you almost have no skillgains and it can lasts for hour, then after very lucky time can be very unlucky or lower than average plato and it can lasts for 1 hour aswell.
I can confirm that sometime power rolls are very strange at first sight. Sometime I get same power, for example 96 power casts on one item almost in row, or yesterday I got 92 power 3 times for 10 minutes on differend items, but before it happened I had unlucky time and did not got any of 90+ power cast for ~130 casts its more than hour of casting, while in average it should happen every 35 casts with two links. But its random and happens fairly rare, everything can be, you got 8 power three times in row, and this is small chance, also as get 100+ power from first cast, but it happens.
Skillgain chance grapths
My current skillgain chance 34% for 10 hour scope looks like this(grapth below). Every point on this grapth represent one cast and its show skillgain chance for last 10 casts, and summary here 709 points/casts. So any spikes on such graphs close to 70% means many low power casts in row, but it compensated by good casts in future, and for long period of time it become stable average 34-36% between days. This is how pure random works, and here is nothing weird to see many bad casts or many good casts in row.
Your average casts on 78 channeling with two links should be 25 power, that explains why most of the time you will see low power, actually you must be happy because its ideal for grinding.
But why you got same power casts in row, lets see.
Chance to get 100 power cast are 0,00018%
Chance to get 8 power cast are 1.2%
Chance to get 8 power 3 times in row are 0,0001728%
This calculations in grinder calc service are rough, and numbers there are not absolute and can be differend between times, but no such big difference between 0,00018% and 0,00017%, right? So we can't tell that is sumething unreal since we many times seen 100+ casts.