Black inks can be exciting! I'm sorry there was an issue. Yes, contact them, if it persists. Hopefully, the disassembly and cleaning remedied the problem. Keep us posted.
Here's the long overdue follow-up. I contacted them and they sent me instructions on improving flow. It didn't help, so they sent me a new feed almost straight away. Meanwhile, I got pretty frustrated having the pen just sitting there, so I grit my teeth (pulling out the nib and feed required a lot of force, scary) and pulled the nib and feed out, soaking the feed in lukewarm water with dish soap and scrubbing it with a toothbrush. It helped, the pen now writes nicely. After filling it, it gushes terribly though, unless I don't completely fill it and turn it upside down to suck the excess ink from the feed with the piston. The pen does seem to run a little dry after a page or so of constant writing, making the ink a little lighter, but nothing bothersome. I might switch the feed I received after my exams, to see if it makes a difference, but for now, I'm okay with it. I have been using it a lot, it's a workhorse with a robust feel to it. It gave me a lot of frustration, but it worked out in the end.
Not sure I'd go for another TWSBI anytime soon, but I must say they handled it very nicely.