Who is responsible for an apartments balcony leaseholder or freeholder?

Maintenance

I have a 2nd floor apartment in a block of 12 which all have glass surround balcony's. One of the glass panels shattered over the weekend discharging glass fragments on the ground below which happens to be near to the front entrance of the building.. The thing is some of the shattered glass panel still remains Insitu and needs to be secured before anyone gets injured. My tenants were away, when it smashed and came home to discover the damage and immediately contacted me. They are good tenants and I do believe them. The other flat owners raised the issue on our WhatsApp group but nobody heard anything so it is unlikely to be malicious vandalism. We are all clueless on how this happened. One school of thought is it could be due to expansion even though it hasn't been unusually hot. Another opinion is it may be something to do with settlement as it is a fairly modern building 2019. Can anyone else put forward a probable cause. I raised the issue with the management agent who have told me that the balcony is not their responsibility and I would need to get a contractor to replace the glass panel. I am not happy with their response. I just wanted them to send someone to make it safe for anyone entering or exiting the building.

Who's is ultimately responsible for the balcony freeholder or leaseholder?