Foster fitting trouble?

I'm a newbie with an FX Impact and I ordered along with the rifle a DonnyFL Stainless Steel Extended Quick Disconnect with Foster fitting because I had read that they are needed on the Impact because the male foster fill port is deep within the trigger guard. I have a shoebox compressor on loan and I'm almost certain I used the Extended QD fitting to fill the rifle after I received it.

Today, I tried to fill the rifle again and the extended QD fitting's collar won't seat in the locked position. I even pulled the trigger guard (4 screws) to be sure it wouldn't. No joy, I couldn't get it to seat. Since the trigger guard was off I was able to fill using a standard length QD foster.

Anyone ever experience a troublesome fitting? I looked to be sure there wasn't some debris or other obstruction. No contact on the walls of the trigger guard. I'm stumped because I'm nearly positive I was able to use the extended fitting for that fill. 
 
I have found that these connections vary slightly from manufacturers . If you look at and measure the male components clearly there are minor but significant differences. I’ve been buying and using connections from Best Fittings UK. A little more expensive but where possible I’ve switched out the male components. I’ve also carefully reshaped them to allow the female extended quick disconnects to slide into place easily. The male connection on my FX is tight compared to the daystate products 
 
Here is an example. You wouldn’t think there is enough of a difference but the best fitting goes easily into the female and the one on the right just binds up
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