There is a limit of 6000 offers for event bundles.
That means that, at this time, you cannot have more than 6000 offers per event bundle. Each time you create an event with multiple offers, up to 60 offers are automatically created. You can add more offers, with a maximum number of 6000 offers in total.
If this limit has been reached for one of your events:
Alternative Solution #1:
You can archive the offers that were completed. Archiving will reduce the bundle count and you will be able to add extra offers to your event.
As an example, if you have reached the limit of 6000 event offers and then archive 50 event offers, you will then be able to add 50 more offers to the event.
Alternative Solution #2:
Create a stand-alone/course-connected event bundle every year/every two years, or similar.
As an example, if the offers of your event per year are up to 120, you could create a five-year stand-alone/course-connected event.