I have replicated the issue on 3 different SharePoint tenants and it seems like it's a bug. I have raised the same issue to Microsoft and I will update my answer once I hear back from them.
Update: It's indeed a bug. I received the following response from Microsoft.
I just wanted to follow up with you after our call with some of the
pertinent information we discussed on the phone!
When refreshing an Event being viewed on a Communication site in
SharePoint, the page shows up blank. I was able to recreate this
issue, and a colleague was as well, so it is very likely a backend
I am going to contact our systems administrator to see if there are
any escalations currently bringing this issue up to the engineers, and
will update you with what he finds!
Regardless, I will try to run some backend diagnostics to try and
resolve the issue on both this tenant and my own.
If there's anything you would like to add, please do so in a reply to
Wishing you all the best, Jesse Office 365 Support