The problem

I have a calendar in my Microsoft mail that I wanted to use in HomeAssistant. I exported the ICS file from Microsoft mail and then created a new HA calendar using the option to create based on an ICS file. This produced an error, however when I went into Calendar there was a calendar that had imported. No appointments showed though and then I realised that HA had stopped responding.

HA Restarted itself and when Up I went into the calendar to check if this had added the entries. It had not, but then HA restarted again. This pattern continued with a short period of function and then a reboot. Eventually I managed to delete the added calendar (not easy from the calendar and it took me a while to figure it out). Once deleted everything returned to normal.

I then re-exported the ICS and attempted to do this again, assuming maybe the ICS file was bad. This resulted in the same reboot loop so I removed the calendar again.

What version of Home Assistant Core has the issue?

core-2025.2.2

What was the last working version of Home Assistant Core?

core-2025.2.2

What type of installation are you running?

Home Assistant OS

Integration causing the issue

Calendar

Link to integration documentation on our website

No response

Diagnostics information

No response

Example YAML snippet

Anything in the logs that might be useful for us?

I do not believe so.  There were no errors or anything and the log itself is cluttered (something just discovered that I need to address!)

Additional information

The calendar I was trying to load is circa 60 repeating events that repeat every 9 weeks (my wifes shifts). If I need to share this I can however as it would give access to those shifts I am reluctant to do it on a public platform.