You didn't really make that big of a mistake. The generic auto caps were a known good substitute until recently. Evidently either the design or quality has changed and now are not a great choice. Stick with the Triumph one and they are known to fail over time, so might just be time for yours to be replaced.
Do you have the service manual? There is a procedure for ensuring air is out of the system. I can look it up if needed, but essentially involves ensuring the level in the filler neck is even with the bleed screw. If one is lower than the other it is a sign of an incomplete fill.