I'm fairly new to chess. I'm practicing against 1500~ rated opponents/engines on chess.com. My openings and middlegame seem to go well. After every game, the engine analysis says I'm always up +1 ~ +3 for the majority of the game. But at the end, I always seem to lose by a blunder. Every game is a "giveaway" according to the analysis engine.
It seems my trouble is actually converting positional advantages. Do you have any tips or areas I should study to avoid this? Is this a stamina issue, as in I start to lose concentration as the game goes on?