2nd event not saving

On opening a scheduler page the first created event behaves as it has been for 2 years.
If I then try to create another event, whilst the scheduler shows the event as being created the save function is never hit (http trace) so if I refresh the page it disappears.

Any help would be greatly appreciated, it’s driving me insane.

make sure you have set autoincrement id in the database (set Id column as Identity column).
Such issue may happen when you don’t have an autoincrement and on inserting the first event receives the default id value (e.g. 0 for int). When you insert the second one - it receives the same default value and MSSQL rejects it because it has the same primary key as the previously inserted event.
Also, be sure to update the model declaration after you update the database.

If it not helps - please attach a demo project so I could check it