Mike and Tom, as insecure as they were when we worked, suddenly started to warm to this Canadian guy who ........

--- I think insecure might mean something like "anxious", but suddenly they turned out to be very "cordial" towards some guy.... Am I pretty much correct?

Yes. Someone who is insecure does not trust himself to make everyday decisions. He is likely uncertain about what to do in social interactions. Insecure people sometimes have difficulty making friends or doing something different than the normal routine.
Your description of "cordial" is good, but it is more than just "polite" - it means they are attracted to forming a friendship.
You have it. To be insecure is to lack confidence. It's usually a "social" phenomenon, but could involve work skills.

I don't get the "when we worked - suddenly" contrast. (assuming the band) they were insecure on stage? The Canadian guy wasn't with the band? (doesn't matter, I guess.)

Edit. A.Stars seemed to pick up on this too. (insecure when we worked) musically insecure or socially insecure?? They were friends with each other but not the rest of the group? The Canadian thing is offstage??
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They were insecure when they worked in the studio, but suddenly started to warm to some Canadian guy who was their producer

Thanks for the answers
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