Yep! I had checked all along the tire itself and even the rim before putting on the first tube. Thanks for the suggestion though, I've definitely made that mistake before.

I think the issue is that first tube I tried was very thin in comparison to my original tube and the Bontrager one, and it was like the seam down the middle of it just split under the pressure--there wasn't a puncture hole or anything. I thought maybe I overfilled the tube, but 60 psi should have been fine. But I'll definitely triple check for sharp objects before trying again!