Problems with the recording calls

I have Asterisk PBX and have encountered the following problem:
After recording some conversations I observe delays between two channels (caller and receiver) in the voice record file, even though on the moment when they are calling, they have a proper communication. This happens when internal users calling to externals.
Recording calls via MixMonitor:

Structure is:
Users [Sip-phone: twhinkle] -> (SIP) -> Asterisk -> (DAHDI) -> Provider.

Using card: Yeastar TDM 16xx

Can you tell me what is the reason of this problem?
Thank you!

Update: this problem is also observed in the original wav file