This appears to just be a visual bug - I was curious and checked just now and I was able to craft it even though it's not showing up as unlocked on the pattern/catalyst screen.
I'm not 100% sure, but I think this happened because I already had a red border Taipan-4fr when I started the quest to get the free patterns at the Enclave/relic, and I somehow skipped a quest step.
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Oh my goodness, I have the same problem with the Ammot AR2 auto rifle. Tha is for the info, I thought I couldn't craft 1.