Hi Ivan,
I tried your formula and I saw the correct result in both my lists, here’s a screenshot for your reference.
Though it shouldn’t matter but just for the test purpose, could you please switch your affected list experience from classic to modern? There are some instances where we got feedback from customers saying some functions are not working in classic view but switching to modern works and some said, it works in classic but not in modern, I just wanted to check if this is the scenario in your case.
To use the modern experience just for yourself, select Exit classic experience in the bottom, left corner of the page. To return, select Return to classic SharePoint.
Please Note, Exit classic experience option is not available if default experience is set to Classic experience.
The formula you are using is correct, please check the Column settings to confirm if you have selected Single line of Text as a data type and whether you have applied any formatting or not.
Besides, please try re-creating the same column with the same formula in the affected list and see if shows the correct result.
Let me know the status.
Regards,
Neha