@jazz78 You’re more than welcome to try to figure out how it ended up with corrupted value inside of dataset.
And if possible, see if you can reproduce from scratch. That would help me a lot.
Have a look at this issue for how steps-to-reproduce can look (that issue is not related to your problem at all).
When you’ve migrated away from H2, then you can try to find all the metabase belonging to the problematic field, and try to delete those rows (make sure to have a backup first!)
You should be looking in metabase_field and metabase_fieldvalues