Given you're feeling pretty comfortable with him, and he's open to talking about things... I think I'd (personally, just me!) stick it out a bit and keep talking.

It would likely be easier if you knew what was causing the problem (like, if there was something specific you could point to - i.e. "T, it's hard to open up when you keep interrupting me - it makes me feel shut down and less likely to talk at all!") - but it's not necessary (b/c we don't always know the problem).

Do you think it could be some sort of unconscious defense on your part? I've been thinking about psychoanalysis lately. I don't know a lot about it, but I believe a big part is that a lot of what we go through comes from our unconscious, and part of that is our unconscious helps "protect" us from bad feelings (like the type that might come up if you started to talk about past traumas)... one way it might do that is make you feel bored or "blah" with your therapist, as a way for you to quit therapy or think it's not helping... thus painful feelings successfully avoided!

(I've been thinking about this, b/c I'm starting to catch on that my unconscious is possibly quite clever, and very heavily defended! )

I might be way off though... just something to think about!

Did your T not have anything useful to say on the subject? Could you tell him you're feeling honestly confused by what's happening, and would like his help in figuring it out? I'd describe what you feel/notice, and ask him if he has any ideas/theories on what might be going on... Maybe directly tell him, "I'd like to do more work around some of my previous traumas... but here's what's getting in the way. What do you suggest for an approach?"

Just some more thoughts... I hope it works out for you!