manage port in router for PBX

We got an issue with our PBX. Our SIP trunk provider indicates that our router blocks some traffic from his IP. We need to fix this. The router works well for many months without any issues. hardware: Mikrotik V6.48 RB3011UiAS PBX grandstream UCM6204 , up to date I join a pcap file with the issue. See example at line 15912, 15917 and many other lines. The PBX work well during about 18 minutes after this the issue happen and we need to reboot the PBX.