@andrewh using the JSON import will result in loss of data, the correct way would be to use an H2 restore file that is generated by the backup procedure. When the JSON import is used the data point will get a different table id compared to what it was originally. The NoSQL uses this id as it is the fastest way to find a row in the table.
@mseverin There are a number of forum threads on how to delete events through the H2 console. By searching "delete events"
These help docs will also be helpful: