Still confused about online fail of GPUs for < W class

So I have tried to read up on this (in FlyerTalk) and become as knowledgable as possible before posting. But there are so many posts on the topic, I am more confused than when I started.

I am trying to use GPUs for the following 6 legs (I am 1K):

IAH-HNL (3 class 777, 33 of 49 Business seats showing avail)
HNL-SFO (2 class 777, 31 of 36 Business/First seats showing avail)
Booked in K

IAH-HNL (3 class 777, 39 of 49 Business seats showing avail)****
HNL-IAH (3 class 777, 35 of 49 Business seats showing avail)
Booked in K

EWR-LAS (737-900, 18 of 20 Business/First seats showing avail)
LAS-EWR (757-200 old United, 23 of 24 Business/First seats showing avail)
Booked in S

In all cases, except for the one marked with **** it is not allowing me the option to use a GPU online. It says "waitlist only." At first I thought it could be a capacity issue, but based on what everyone else here says, that's not the case. I am understanding that, basically if there is even one seat left, you can get it using a GPU.

I've been reading that UA.com *still* is basically not allowing anything below W to upgrade online using a GPU. Apparently it is working for some (and 1 out of 6 for me), but not for others.

Is it really as simple as calling the MP line and hoping to get an agent who understands that GPUs can be used for USA-HNL flights in any fare class? Or am I missing something? Could there be a capacity issue here??

Guess I am just wondering why they wouldn't have fixed the online issue by now if that's the real problem. Doesn't seem like a tough fix.

Thanks for any advice.