Blue Tits in my camera nest box abandoned their 5 babies after just 2 days. Why?!

On Thursday last week 2 baby Blue Tits hatched out of a nest of 5 in my camera nest box. Friday 2 more and Saturday last egg hatched. All doing really well, both parents feeding. On Sunday I did not see the male visit in the morning but female was brooding. In garden all day and didn’t notice much activity in and out of nest box. About 4 o’clock saw a parent fly out of box. 6 o’clock turned on camera and no parents in box, babies alive and asking for food. No parents returned by 8 o’clock. Babies all dead Monday morning. Devastated. What happened??!!