When you break off on a fish, the vast majority of the time the knot, or a critical nick within the first 3 ft of line. That or the fish has you between an object. Depending on the oldness, or level of abrasion on the line, as mentioned above, a nasty 2lb Bass is gonna break off 6lb test especially.
Outside of some really rare occasions, I won't use 6lb test for any Bass applications. 8lb test on spinning reels has always been my personal cutoff for Bass finesse setups, especially with the quality Fluro type lines these days. I can easily break 6lb test with just solid hand pressure. That's always been my "redneck test" since I was a kid lmao.
My best fish this year came about two months ago.....right at 8lbs. Two nights later I break a really nice fish off in clear open water, get a quick glance at it enough to realize it was indeed gonna be a real high quality fish. After I finally stopped busting myself up over it for a few days about how that was for sure next DD fish you lost, I reminded myself of the advice I just gave you. The reality is that I was likely sloppy.....had caught at least half dozen Bass on that rig without cutting off a few feet and retying the rig. I knew better, and I likely cost myself, rather than my actual tackle.
The best big Bass fisherman I've always known preach two things........knot quality/checking, and checking the first few feet of line after every fish, feel a single thing in those feet, off they go and you retie the bait