We went through something similar before and honestly toddlers can be so unpredictable 😅 One week they’re happily running into school, the next week they’re clinging and crying at drop-off.
For us, it wasn’t necessarily because something bad happened. Sometimes it was a developmental phase, separation anxiety, a change in routine, a new teacher/classmate, being overtired, or even just becoming more aware that mummy/daddy is leaving.
I would continue talking to the teachers and observe whether your child settles down shortly after you leave. If he’s happy and engaged after a few minutes, that’s usually reassuring.
Trust your instincts though. If the behaviour persists for a long time or you notice other changes (fear of a specific person, nightmares, refusing to talk about school, sudden behavioural changes), I’d keep probing gently and ask the school for more detailed observations.
Parenting toddlers really keeps us guessing sometimes 😅❤️