ASM Re-enable Learning for Blocking Mode Policy

we have ASM policy already in blocking mode for a while. recently file upload has been enabled on the web-application however ASM is blocking all file-uploads with multiple violations for each upload

attack signature

HTTP compliance

Evasion techniques

ect..

what would be the best approach to fine-tune the policy , we have tried to change it to transparent however the learn button is still disabled and we are not getting new suggestions.

please advise