Maybe give it a tap IN direction to free the cap. Make sure there is not a ridge of build-up that is blocking, or a lip on the clip ring groove. I think the spring should push the cap out. Maybe a good strong magnet. A new o-ring is called for. Maybe a new spring too.

 

So it feels good to be right, at least so far. I had a chance to dig into my oil pressure issue and found the small o-ring inside the filter adapter housing was broken. That was my guess. When I replaced it two years ago, I matched it with an o-ring from Napa and was told it was oil resistant. This thing was pretty brittle, so that wasn't right or it wasn't heat resistant or both. Maybe 8k miles on it. After replacing it with an OEM o-ring all appears to be normal, with a slight twist.
When I had the oil pressure sit-at-zero issue on cold start, when it did come on it held stronger numbers once warmed up. So even after a highway run in the 100 temps we had it would hot idle at 25-30 psi. Now it behaves more like before and idles at around 12 psi when hot. I am OK with that, it's in specification and my engine has 180k on it. So whatever that o ring does, when broken it can cause zero cold start pressure randomly and stronger hot pressure when it decides to work with a hole in it.
The best I can tell is that it seals between the front cover cavity (pressurized post pump) pre filter and the post filter cavity (center pipe) as the oil heads up into the engine. Also pressurized.
Curious what the pro's here think is going on.

 

How would that broken o-ring cause a pressure drop?Some oil bypasses the filter, pressure should not drop.

 

I have no idea, and not 100% sure that was the problem. Time will tell.