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Have you synced your Steamgifts account to Steam?
If yes, and that should be the case if you are talking about the group, you promoted a while back, than it is a bug that probably fix itself in time. This might be hours, this might be months. As far as I understand it, it is an issue with Steam's API, nothing that can be done from the Steamgifts side of things.

I've seen people complain about this before. The answer is Steamgifts periodically updates all groups. You just have to wait till that happens. Syncing you own account does not add the group to steamgifts. You add yourself to the (Steamgifts version) group, but Steamgifts need to sync first for the group to show up.

If it's anything like other sync bug people experience here, it might help to actually logout and log back in on steam webpage and here and then sync again

I know at least of one other group having the same problem - Under500.
Hopefully SG syncs up with Steam soon, though the admin @Under500 told me there were even newer groups that had already been recognized by SG .. who knows what gets the API flowing !? : /

Of all the 56 groups I'm in (according to Steam), SG only misses 2 (CiroooGiveaways & Under 500 club), both of which were created at the end of January 2021. SG does however also list 5 groups that disappeared from my profile's group list at some point and can't be found by Steam's search function either.
My guess would be that SG creates an own cached list of all groups (or all groups that they found in SG users' profiles) at certain intervals, and just hasn't updated it since. It's almost 2 months, though, and I wouldn't rule out the possibility that SteamAPI returns outdated data or that SG doesn't query some specific data because it THINKS it's up 2 date.

Depending on what the actual issue is, there MIGHT be a way to, kind of, kickstart an update process...

What I would try first:
(Just to be sure and rule out any parse errors from the description (which may or may not be included in the response to SG's API request))

• Delete the whole group description text (keep a copy of course, so you can undo it if it doesn't work)
• Wait
• Re-Sync on SG and see if the group finally shows up in your account data

Dunno if it works, but this might also be worth a shot:

• Head over to Steam and make a substantial change to the group (group name, application/join method, group visibility or sth like that)
• Wait 24 hours (might even update instantly or within an hour, but just to be sure)
• Undo what you changed
• Re-Sync on SG to see if the group finally shows up
  Maybe that will mark Steam's internal group data as "dirty" so that the next API query doesn't return (outdated) data from cache?

It seems it happened before, and actually multiple times. So, I guess all we can do - is wait for cg to come and fix, when he will have some spare time.