Copying lookup column value error

Hello Community,

Is there a way to copy a lookup column value of one item to another item in the same column and library (in SharePoint Online)? Right now, if I go into grid view and try to drag one row's lookup column value from the bottom right corner down to other items in the same column I get an error that says: "'[COPIED VALUE] is not a valid value for this field." Same result if I copy and paste the values.

Is this a limitation of SPO or am I missing something here? I feel like this has worked normally in the past. See screenshot below for more details.

Thanks!