Problem with sharing audio files through WhatsApp in Lumia 720, can I get some help?

[Windows Central Question]

Problem with sharing audio files through WhatsApp in Lumia 720

I am using WhatsApp in my Lumia 720 phone. Since last couple of days, I am facing problems in sharing audio files (recorded directly in WhatsApp in my own mobile) with some recipients. They are not receiving these audio files from me though in my chat history it shows as delivered (two grey tick marks). But a few other recipients are able to receive the same audio file from me. Strangely, some of these recipients who are not able to receive it when I send it to them individually, are able to receive it when I send the same file to a WhatsApp group in which they are part of. But a few of them are not able to receive it even when sent to the group.

I am facing this problem only since last 2 days. It used to work without any issues before that. I updated WhatsApp to the latest version available for my phone, but still the problem persists.

My phone details below:

Model: NOKIA Lumia 720
Software: Windows Phone 8.1 Update
OS version: 8.10.14219.341
Firmware revision number: 3058.50000.1425.0002

WhatsApp version: 2.12.344