We have identified an issue with the 2.1.0 Beta 1 upgrade that could cause data to not be properly converted to JSON during the upgrade process. This may cause errors or some data to not be displayed/processed correctly. We will be releasing Beta 2 tomorrow (Wednesday) to resolve this issue.
Because of the nature of the problem, it will not be resolved if you already upgraded to 2.1.0 Beta 1. Our recommended resolution would be to restore to a pre-upgrade backup and re-upgrade once a fixed release is available. Therefore, if you have not already done a test upgrade, we recommend holding off until Beta 2 is released.
For more specific details on the bug, please see this bug report:
Fixed - Serialised content array not converted to json