As the title suggests, while I'm having a battle with my friend, the issue that is related to No Guard ability just happened.
I sent out my Pidgeot, let it mega evolve and chose move: Hurricane, my opponent sent out his Torkoal whose ability is Drought and chose a move. Then the mega Pidgeot's Hurricane missed.

Here're some simple tests for the issue, produced by pokemon editor:
test 1:
My pixelmon: mega Pidgeot(No Guard)
Opponent pixelmon: Torkoal(Drought)
mega Pidgeot use Hurricane→miss
mega Pidgeot use Thunder→miss
mega Pidgeot use Dynamic Punch→hit accurately

test 2:
My pixelmon: Machamp(No Guard)
Opponent pixelmon: Torkoal(Drought)
Machamp use Hurricane→miss
Machamp use Dynamic Punch→hit accurately

test 3:
My pixelmon: Pidgeot(Big Pecks)
Opponent pixelmon: Torkoal(Drought)
Pidgeot use Hurricane→hit sometimes
Pidgeot use Dynamic Punch→hit sometimes

From the tests you can notice that only moves whose accuracy are affected by weathers will miss under the ability: No Guard.
One more thing you need to know is that, I've tried 15 times to let a No Guard pixelmon use Hurricane in a sunny weather, but it all missed. I guess that the accuracy of moves like Hurricane and Thunder in a sunny weather might would be 0 in battle.
I've tried ability Trace which is produced by Gardevoir to mega Pidgeot, it's ability is No Guard without any doubts.
This is not a serious big problem, hope that you could solve it breezily. :)

The third-to-last paragraph is not very accurate. I mean that I guess the accuracy of moves like Hurricane and Thunder in a sunny weather under the effect of ability No Guard might would be 0 in battle.

Late but, Was able to replicate Mega Pidgeot Missing Hurricane in drought. Ss still a thing in later builds and 8.0.2, I'll notify the team and hopefully, they can fix this.

Thanks for reporting tho!

Thanks for the report. I've now moved this to our internal tracker, and we will update this ticket when we know more.