Hello treecarer,
Thank you for reaching out in Apple Support Communities. Is the account that you're using for your calendar events with iCloud or a third party email account? A step that may help is to temporarily turn off the account you're using for the calendar events and then restart your iPhone. From there, you can turn on the account that you're using for the calendar events and see if the reoccurring calendar events remain deleted.
To turn off and on the impacted account for calendar on an iPhone, you can go to Settings > Calendar > Accounts. Then select the account you're using for your calendar events and turn off "Calendars." If you're using iCloud, it would be Settings > Calendar > Accounts > iCloud > iCloud > Show All > Calendars.
We look forward to hearing back from you with an update.
Kind regards.