That is a mystery. Are you using the same color cup/bottle in your tests? And the same side feed. I'm thinking about clogged side feeds here.
Very unlikely, but is the needle locking nut in all your tests fully tightened? And does the needle move in and out when the trigger is pulled?
Pressure changes between test? Have you run a very fine wire through the tip)s) that don't work.
Will plain water go through the 0.35mm tip?
I don't have an answer...I'm just giving you some ideas to explore.
If no others have the solution, maybe e mail