Eleven of the last fourteen leads at half time were surrendered. That is not variance. That is a division that has decided, collectively, that a one-goal lead is a problem to be solved by scoring another.
The numbers
Teams leading at the break are winning 54% of matches this season, down from 71% five seasons ago. Expected goals conceded in the second half by leading teams has risen every year in between.
// Leading at half time
54%
Win rate, this season
71%
Win rate, five seasons ago
+0.4
xG conceded after the break, change
Why
Because the coaches were hired to press, and pressing is a thing you do with the ball or without it, not a thing you stop doing at 1–0. The block that used to protect a lead is now a formation nobody has practised.
The exception
One club. They have not conceded a second-half goal from a winning position all season, and their manager is the only one in the division who was a defender.