I am also experiencing similar problems with my unraid server, however I have an intel NIC built into my skylake board, and according to unraid, it's:

 

Ethernet controller: Intel Corporation Ethernet Connection (2) I219-V (rev 31)

 

I am running the latest unraid version 6.1.7

 

I have attached a picture, so you can see what I mean....

Are those pings from wired or wireless PC? Wired pings are usually <1ms.

I split your post off to here, because there are many reasons for network timeouts and delays, and the other topic seemed more related to driver problems, with the Marvell driver.  Because your post now starts the topic, you may wish to edit the first sentence.  You may also wish to include Diagnostics here, see Need help? Read me first!.

I am also experiencing similar problems with my unraid server, however I have an intel NIC built into my skylake board, and according to unraid, it's:

 

Ethernet controller: Intel Corporation Ethernet Connection (2) I219-V (rev 31)

 

I am running the latest unraid version 6.1.7

 

I have been having lots of trouble with my unRAID networking, with lost connection to the box, VERY unreliable SMB, etc -- and my motherboard has the same Intel NIC as yours.  As a troubleshooting step I added a separate Intel PCIE Ethernet card (disabling the one on the motherboard) and my networking experience has been vastly improved.  I can't tell if it's solved the unable to connect issue, but I can say that SMB is working so much better than before that I'm sure that my built-in NIC is either bad or has a driver issue.