Update: I figured out a workaround even though this is not a permanent solution.
Before I did copy existing profiles which results in the same problem. However, by adding a new profile and re-assigning the keys from scratch the macro seems to work.
If there was not a bound key on the Tartarus before, I can assign a macro no problem. But as soon as I try to switch it out after assigning a button once, it simply refuses to accept a macro on that key.
Very weird. I hope this can be fixed, but this works for now.
I have the same problem as almost all my colleagues who have Tartarus Pro, you can't change macros, the first macro that was set always remains, I'm super annoying because I can't make any changes, if I make a mistake I have to create another profile and set macros to all the keys again... I hope for a solution from Razer, otherwise I won't buy any Razer product again...
Someone posted a solution outside of Razer website.
He shared that there is a new Synapse software (albeit Beta version)
https://www.razer.com/au-en/synapse-new
It worked for me but you will have to backup all your macros by saving them individually via Export) and taking a screenshot of your macro profiles and keybinds as everything will be wiped and you will not be able to import any backed-up macros via Local/Cloud.