BUG Whatsapp IOS

Hi, unfortunately I have to report a problem on Iphone 12. 
When playing voice messages on Whatsapp with the screen off, they tend to croak. 
While with the screen on, the problem does not occur. 
I have already contacted Apple for clarification but after careful technical checks, 
hardware and software no anomalies were found. 
So it would seem an APP optimization problem with IOS. 
How could this annoying bug be fixed?