Hi, I started to have the same problem yesterday: after weeks without any problem, suddenly I started to receive the following emails:
[ERROR] Can't update blacklist repository: fetch failed
I’m using firehol/block-list ipsets and it seems that at some point an IP address from github (140.82.121.4) was included in some of the ipsets (specifically blocklist_net_ua and firehol_level4).
To solve it, from nethserver terminal I did:
ipset add bl-whitelist 140.82.121.4
/usr/share/nethserver-blacklist/download ipsets
I had to do that from the terminal as adding the IP address to the whitelist from the web GUI and even removing the category complained about the blacklist repository, maybe because it was trying to download the ipsets before applying changes.
After that, I finally added github IP address to the whitelist via web GUI and everyting worked fine.