*** NetChannel (21) refused a packet

[Linkorz 0]

I'm trying to pin down an issue with a long standing Arma 3 server. Until recently, the server was working fine, but over the last 2 days we have been experiencing a lot of desync and lag. Trying to get to the bottom of this, I have enabled -netlog on the server and reviewed the output, but I am approaching the edge of my knowledge. I  suspect that the below is a symptom of the issue, as it full of entries like this, however I am not entirely certain what NetChannel is and how to find out why it is refusing packets. Is this an application at the software/OS level, or a network level item?

 

The server is on a Windows 2016 OS, itself running as a VM on a proxmox install.

 

I have confirmed that pinging with "-l 1400" works and the MTU isn't set in the config, so it should be on the default of 1400 if I'm correct.

9610.145: Ch(21):sRetry(240,437359,7000.00)
 9610.153: *** NetChannel (21) refused a packet: serialID=235512 (206193...235915), IP=81.97.xxx.xxx
 9610.158: Ch(21):sRetry(288,437686,5190.28)
 9610.168: *** NetChannel (21) refused a packet: serialID=235513 (206193...235915), IP=81.97.xxx.xxx
 9610.175: Ch(21):sRetry(80,437689,5190.28)
 9610.185: Ch(21):sRetry(80,437836,3707.35)
 9610.188: *** NetChannel (21) refused a packet: serialID=235514 (206193...235915), IP=81.97.xxx.xxx
 9610.204: *** NetChannel (21) refused a packet: serialID=235515 (206193...235915), IP=81.97.xxx.xxx
 9610.219: Ch(21):sRetry(80,437064,7000.00)
 9610.220: *** NetChannel (21) refused a packet: serialID=235516 (206193...235915), IP=81.97.xxx.xxx
 9610.231: Ch(21):sRetry(32,437358,7000.00)
 9610.231: Ch(21):sRetry(80,437691,5190.28)
 9610.243: *** NetChannel (21) refused a packet: serialID=235571 (206193...235915), IP=81.97.xxx.xxx
 9610.249: *** NetChannel (21) refused a packet: serialID=235572 (206193...235915), IP=81.97.xxx.xxx
 9610.278: *** NetChannel (21) refused a packet: serialID=235289 (206193...235915), IP=81.97.xxx.xxx
 9610.290: *** NetChannel (21) refused a packet: serialID=235291 (206193...235915), IP=81.97.xxx.xxx
 9610.296: Ch(21):sRetry(80,437755,4448.81)
 9610.303: *** NetChannel (21) refused a packet: serialID=235292 (206193...235915), IP=81.97.xxx.xxx
 9610.303: Ch(21):sRetry(80,437756,4448.81)
 9610.309: Ch(21):sRetry(48,437761,4448.81)
 9610.317: Ch(21):sRetry(80,437762,4448.81)
 9610.323: Ch(21):sRetry(32,437766,4448.81)