There’s a good article here, based on an interview with Allegri. You’ll need to translate.
https://www.alfredopedulla.com/allegri-ai-calciatori-bisogna-guardare-le-gambe-sono-come-i-cavalli-tattica-e-schemi-tutte-p-te/
Essentially some players are just too confused by tactics. Most will respond to general instructions and thrive but some of the time over complicated tactics will just result in poor performances and failure. Is this what’s happening at Saints right now?
We’ve had three managers in a row with a different set of attitudes and tactics towards the game. Maybe it’s no surprise our least hands on manager tactically has been our best in the past decade (Koeman).