Weird

Do you think it’s due to the acoustics of my listening space?

My guess would be you’re sitting in a null created buy how both subs are interacting with your room and each other.  Try playing with speaker positioning and your listening position and see if that changes things and/or reversing sub terminals on one speaker if possible.  I don’t know how GoldenEar’s customer service is but I’d give them a call too as I’m sure they’ve run into this before.  Best of luck. 

Out of phase

Unfortunately, the subwoofer only has a wall power connection.  No leads to reverse.

Actually, I’m happy with the way it sounds now.

‘But I’ll call GoldenEar and hear what they have to say.

Not sure if this will make any difference, but if the passive radiators are only on one side of the cabinet you might try just switching the speakers to the other side and see what happens.  Just spitballing here.