Well, sir .... I've been using 4lb test mono for over 20yrs, and I don't remember any times I've lost a Crappie from line breakage. I have seen my friends & fishing partners try & lift a big Crappie, out of the water & over the side of the boat, & break the line from doing that ... several times. I was doing the same, with the same line, and boating all of my fish. The difference was, I think, that I wasn't in quite as big a hurry to get the fish in, as they were. Their fish didn't break the line from shear weight, or flopping around .... "they" broke their line from trying to yank/jerk the fish out of the water & into the boat. All of us were lifting the fish out of the water, by holding onto the line.
Since you mention that your drag may have been a little tight ... is that an indication that you lost the fish "fighting" it (during the retrieve) ... or does your statement "while landing fish" literally mean while you were lifting them into the boat ??
In any event, even if you change line brands or pound test .... do yourself a favor : Take a dry Q-tip or cotton ball & run it around the rim of your reel's spool, and the inside of every guide on your rod. If any cotton fibers are removed from the Q-tip or cotton ball .... you've found a knick, that could be responsible for causing damage to your line.
... cp