Hi @trettkowski,
Define Variable did not originally support lists, so the behavior you’re seeing in production, where a list value outputs as empty - is expected. It appears SailPoint has introduced an enhancement that allows Define Variable to handle lists, which is why it works in sandbox. This enhancement may currently be limited to sandbox tenants and has not yet been rolled out to production.
There are a couple of older posts about this - Workflow - Define Variable - Input string has a list - Identity Security Cloud (ISC) / ISC Discussion and Questions - SailPoint Developer Community