Excel no longer opening files with [] in the file name

Since office 365 upgraded to version 2504 our users have been unable to open files with [ ] in the file name. 

Example a file with the name [12004][]_MCH_12004-SSC Pacific.xlsx excel throws the errors 

Basically cutting off the whole file and only finding 12004 now. 

Why was this functionality taken away. We understand that [] is not recommended in an excel file name. We have antiquated systems written in COBAL that auto generate these file with the brackets. 

Older versions of office still can access the files but anyone with 365 can not. 

How can we get this functionality back? 

Nothing in the changelogs for office version 2504 mentions a change to remove this functionality.