It appears that the system is using the SID when using table or explicit sort field with a composite text field rather than the field value. This is probably due to the fact that the SID is what is brought back in the field and the rendering handles access to the field value.
Active
5.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I just found this bug as well. Same issue with a Name field. I wish I could help with code, but just offering a bump/plea for a patch.
Just noticing this also for a name field where I want to sort last, first