Are we talking mental fatigue and a drop in motivation. Because physically they should be well recovered in that time.
I can imagine initially Spurs as a collective were quite excited about the direction they were going in. But they’ve plateaued since then and they realise they won’t be moving forward without additions that they can’t afford right now. That’s going to hit their motivation somewhat. Plus their game was based on intense pressing. It’s hard to maintain that month after month.