System: PC and GOG.
Starting with the last update v2.54 I could no longer connect to the matchmaking service so multiplayer was completely gone. I reported the issue to HG and GOG.
However, a Norton Data Protector notice had been popping up so I checked the history.
Category: Data Protector
Date & Time,Risk,Activity,Status,Recommended Action,Status,Program Path,Program Name,Date & Time,Action Observed,Target
6/17/2020 1:26:26 PM,High,Data Protector blocked a suspicious action by NMS.exe,Action Blocked,No Action Required,Action Blocked,D:\Program Files (x86)\GalaxyClient\Games\No Man’s Sky\Binaries\NMS.exe,NMS.exe,6/17/2020 1:26:26 PM,Suspicious process attempted to open a file protected by Data Protector,“C:\Users\XXXXXXXXX\AppData\Roaming\Microsoft\Crypto\RSA\S-1-5-21-3865389568-4114757165-3109438426-1002\a8f250cd77ad5cb836dd8143ce9ee2ed_32c17bb4-0259-4d09-8290-671187e837e8”
Full Path: D:\Program Files (x86)\GalaxyClient\Games\No Man’s Sky\Binaries\NMS.exe
This appears to be an Antivirus software issue, not NMS.
If you are running Antivirus and can’t connect to the matchmaking service it might be as simple as making NMS.exe an exception to your Antivirus/Data Protection software rules.
In Norton 360 it is simply clicking the “Trust Now” option.
I have sent HG all this information.