Some days you can do nothing wrong, some days nothing right.
That's why it's called fishing, instead of catching.
#50 Lb Might be over kill, but I would look for other reasons for the drops.
Did the fish feel resistance ? Tip up working smoothly?
Did the fish pull the line through some weeds letting him know something was not right?
Lots of things can go wrong.
Here's what you could try:
Take a rubber band and pull off 10 feet of line deeper than you want to fish. Tie the rubber band around your line with a couple of half hitches. open the loop on the rubber band and slide it over the spool on your tip up. re-wrap the line onto the spool by hand to the depth you want to fish, and set up your tip up normally.
Now a fish hits, runs off 10 feet of line, the rubber band pulls on the line (setting the hooks) and then the fish breaks the rubber band and continues to run. Only difference is he can't drop the bait because the hooks have been set.
Hope this helps,
Wiener