When configuring option sets between environments it is important to do the configuration through the user interface in your 'gold' environment and then use import and export to move the lists through to production.

If you manually enter option set values then there is a risk that the sequence number between environments will become out of synchronisation which will cause issues with import / export.

This often manifests itself in errors in the import export process for the import of option sets or option set items disappearing.

How can I check the sequence numbers?

Go to Admin > Diagnostics > Config Diagnostics

View the 'Possible conflict adding new option set values' and hover over the 'i' to check the sequence number.

Check the sequence number in each of the environments.

What should I do if the sequence numbers are out of sync?

Find the highest sequence number and set all environment sequence numbers to that value. This will need to be done via the database and so may require a technical administator.