Hi Daniel,
Good day to you. Thanks for querying in this forum.
According to your description, the LEFT function and the CONCATENATE function don't work properly in your Microsoft Lists calculated column. Very sorry for the inconvenience caused at your end. We deeply understand this issue has affected your daily work.
We also tested from our side, it seems like we cannot reproduce the issue.
For troubleshooting, we'd like to confirm the following information:
1.Which browser are you using? If you try a different browser such as Chrome, Edge, Firefox, does same issue still happen?
2.Does the issue happen in a specific Microsoft list? If you try a new Microsoft list, does it work?
3.Do other users in your organization have this issue? We'd like to narrow down the situation and check if the issue only happens on your side or it's a tenant wide issue.
We appreciate your time and effort. Hope you are keeping safe and well.
Best regards,
Tina