Question

zoiper3 and zoiper5 call cuts off after 20 seconds more often than not, other client software x-lite works fine

Answer 1

Hello,

You should check our article regarding this issue, here: https://www.zoiper.com/en/support/home/article/72/calls_get_disconnected_after_30_seconds

Try to disable the "Open random port above 32000". If the SIP ALG expects the softphone to use port 5060, It may sometimes rewrite the destination ports of the ACK's.