Server ports issue

[Lpsd]

So, I'm having a problem with UDP ports 22003 and 22126 on my MTA server and not sure where else to turn. I'm running CentOS 7 Linux release 7.3.1611, 3.10.0-514.26.2.el7.x86_64

These ports have definitely been opened fine. Players are able to connect & play, then randomly they'll all get timed out and no-one will be able to connect for a random length of time, usually lasting between 5-30 mins, sometimes longer. This has been happening since the MTA server was setup on my machine, maybe a week ago?

During this time, https://nightly.multitheftauto.com/ports/ reports that the ports 22126 and 22003 UDP are closed. 22005 (TCP) is fine. To confirm this I type 'openports' into the MTA server console and it shows 22003/22126 are closed and 22005 open (the MTA server is still running)

Running "netstat -anp | grep 22003/22126" in SSH shows

udp        0      0 0.0.0.0:22003           0.0.0.0:*                           35501/./mta-server64
udp        0      0 0.0.0.0:22126           0.0.0.0:*                           35501/./mta-server64

 

So, it's listening. Next I do "nmap -sT -sU -p- xx.xx.xx.xx" to check which ports are open.

PORT      STATE         SERVICE
22003/udp open|filtered unknown
22126/udp open|filtered unknown

I spoke to my host just recently, they checked everything out and suggested that it could be a problem with the service running on these ports - they didn't find any problems with firewall config or my network. Furthermore these are the only ports effected by this problem, all my other ports are completely fine which have been configured in exactly the same way.

I've tried all the obvious steps, restarting my machine, stopping all custom resources/scripts on my server.

So, I'm wondering if there's a possibility this could be a problem with the MTA server? Running out of ideas.

Any help appreciated.

Edited August 21, 2017 by LopSided_

[Lpsd]

Bumping this.

[Lpsd]

Now I'm almost certain this is a problem with the MTA server

nmap when server is running (even when players cant connect)

[root@server ~]# nmap -sU localhost -p22003

Starting Nmap 6.40 ( http://nmap.org ) at 2017-08-25 16:55 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up.
Other addresses for localhost (not scanned): 127.0.0.1
rDNS record for 127.0.0.1: localhost.localdomain
PORT STATE SERVICE
22003/udp open|filtered unknown

Nmap done: 1 IP address (1 host up) scanned in 2.06 seconds

main thing here being the filtered...

 

Nmap when server off

[root@server ~]# nmap -sU localhost -p22003

Starting Nmap 6.40 ( http://nmap.org ) at 2017-08-25 17:02 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000032s latency).
Other addresses for localhost (not scanned): 127.0.0.1
rDNS record for 127.0.0.1: localhost.localdomain
PORT STATE SERVICE
22003/udp closed unknown

I can't see how this could be anything other than an MTA issue, if it was a problem with my firewall or network it wouldn't just be coincidentally affecting MTA ports.

Anyone?