ical invite attachment

I am using iCal on a MacBook Pro and sending emails via the Mail app - all software up to date. Normally I create an event in the calendar and then click control and select 'Email event' - this opens a new email with an invite attachment which I can then edit and send through the Mail app. I like this because it means I have full control of the email - it ends up in my sent items so I can see it has gone - and the attachment is essential because users of other calendar types can click on it and add it to their own calendars.

But sometimes when I follow these same steps the email appears without the attachment - and I know of no other way to create this attachment.

This is driving me mad - it is making work incredibly stressful because often I will be trying to create and send an invite urgently and I can't add an attachment. Of course I can put the info (Zoom link etc.) in the body of the email but this then has to be added to other people's calendars manually and they are often too busy, so things get missed.

Please, please can anyone shed light on what is going on? I have tried restarting, searching for updates, etc. Nothing seems to help. The calendar is currently not creating attachments and I have no idea if or when it will start to do so again (it has happened sporadically in the past).