Welcome aboard!
Assume you're talking the terminal knot (hook)?
Possible the line is abraded/weak due to various
issues (snags, structure, etc.)?
After an "issue" where the line rubs a dock pylon,
downed tree, bridge, rocks, do you rub your fingers
down the line to make sure it isn't nicked anywhere?
As well, since it's your first time using, can't dismiss
the possibility it's a bad spool...