Replaced GFCI no power in line wire but power in load wire
Hard to say exactly what the problem is. Pictures would help. But here are a couple of thoughts:
Overloads can cause multiple problems
It is possible that an overload at one receptacle can damage that receptacle and also damage wires in other locations. In particular, if you have a string of receptacles, something like:

Breaker
Receptacle - Living Room
Receptacle - Bedroom
Receptacle w/GFCI - Lanai

then an overload at the GFCI could cause problems in the living room or bedroom receptacles. This is especially likely if those receptacles are functioning as part of a chain - power in on left and out on right (or vice versa) and the connections are done with backstabs rather than screw terminals. If you had a weak connection before, an overload may have made it weaker.
Breaker Mismatch
&quot;15amp breaker&quot; plus &quot;Leviton 20a dual pole&quot; is against the rules and a Really Bad Idea. The other way around is OK - 15A duplex receptacle on a 20A circuit.
The problem is that when there is a 15A breaker, it is there to protect wire (normally 14 AWG) that is rated for no more than 15A. By installing a 20A receptacle, you are encouraging use of larger appliances (as was the case here). While the breaker should provide enough protection, using a smaller breaker than the receptacle can lead to nuisance trips and a temptation to swap the breaker (without making sure all the wire is 12 AWG or larger), as well as other problems. This should be a 15A dual receptacle, not a 20A dual receptacle.