Recorded audio is choppy with openvpn

hello Dears,
I have a problem with recorded calls.
endponint 1 uses openvpn connection to my Fortinet Firewall then register itself to freepbx
endpoint 2 uses local netowrk behind the firewall and registered directly to freepbx
call quality is normal when two end points are talking
but after channel hang up when I play the recorded audio between these 2 endpoints
the audio coming from endpoint 2 is choppy. audio from endpoint 1 is normal

there is a fact that there is no problem with recorded calls in local network they were played normaly with no choppy sounds!

could you tell me the possible reasons?

thanks