This happens when momentum is running against you in a game. When you are one of the top teams in your division they all come for you. Your players need to be sharp and fully rested to compete freely. On away days, this may still go against you and you need to prepare. If your subs aren’t making an impact you need better subs. Sometimes older players just can’t keep up with the demands as the stamina falls or they take longer to get to full sharpness, these players need to be sold. I struggled for a long time trying to bend the game to my will, to force players I wanted to be good but weren’t ready or were past their prime to win time and again. Try to change and see where the improvements take place.

Damn I saw this 5 months later but I'm glad I did, I'll put it into practice on my next save

Try to replace your oldest player or your lowest overall starter at the start of each season. It’s good practice to keep your squad improving every season.

I think the game uses that to force change, I’ve noticed that after 2-3 seasons without a tactics and or squad overhaul. Once you switch things up the team will feel rejuvenated