Interestingly, I got tired of having this visual annoyance in my games list, and when I deleted local content and tried to reinstall, I encountered a similar issue, which happens to have been just recently added to this issue tracker: https://github.com/ValveSoftware/steam-for-linux/issues/2871
What he describes there fits my symptoms perfectly, now - I'm guessing that it's probably the same root cause that was getting in the way of my update issues as well.
I've mentioned something very similar over in the other bug I mentioned above, but when I look back at my old content_log.previous.txt, I can see the following when it had been trying to update X3: Reunion:
[2013-09-23 10:34:50] Scheduler update appID 2810: Priority Last, legacy=no, restore=""
[2013-09-23 10:34:50] AppID 2810 state changed : 0x00000106 = Update Required,Fully Installed,Update Running,
[2013-09-23 10:34:50] AppID 2810 state changed : 0x00010106 = Update Required,Fully Installed,Update Running,Reconfiguring,
[2013-09-23 10:34:50] Got 20 download sources via "/serverlist/95/20/" from 209.197.20.102:80
[2013-09-23 10:34:50] HTTP (CS,86) - valve100.cs.steampowered.com (valve100.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,114) - valve181.cs.steampowered.com (valve181.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,28) - valve199.cs.steampowered.com (valve199.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,129) - valve42.cs.steampowered.com (valve42.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,130) - valve43.cs.steampowered.com (valve43.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,128) - valve11.cs.steampowered.com (valve11.cs.steampowered.com): OpenConnection - Success!
[2013-09-23 10:34:50] HTTP (CS,128) - valve11.cs.steampowered.com (valve11.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:34:50] HTTP (CS,86) - valve100.cs.steampowered.com (valve100.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:34:50] HTTP (CS,28) - valve199.cs.steampowered.com (valve199.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:34:51] HTTP (CS,130) - valve43.cs.steampowered.com (valve43.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:34:51] HTTP (CS,114) - valve181.cs.steampowered.com (valve181.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:34:51] HTTP (CS,129) - valve42.cs.steampowered.com (valve42.cs.steampowered.com): AuthenticateDepotID (229330) - ERROR: HTTP response 403 (Forbidden)
[2013-09-23 10:36:50] Update job for app 2810 canceled: missing manifest 6909182178174349347 (Connection timeout)
[2013-09-23 10:36:50] AppID 2810 state changed : 0x00810106 = Update Required,Fully Installed,Update Running,Reconfiguring,Update Stopping,
[2013-09-23 10:36:50] AppID 2810 state changed : 0x00800106 = Update Required,Fully Installed,Update Running,Update Stopping,
[2013-09-23 10:36:50] AppID 2810 state changed : 0x00000006 = Update Required,Fully Installed, (Connection timeout)
[2013-09-23 10:36:50] Scheduler finished appID 2810: removed from schedule
[2013-09-23 10:36:50] HTTP (CS,86) - valve100.cs.steampowered.com (valve100.cs.steampowered.com): Closing connection
[2013-09-23 10:36:50] HTTP (CS,128) - valve11.cs.steampowered.com (valve11.cs.steampowered.com): Closing connection
[2013-09-23 10:36:50] HTTP (CS,114) - valve181.cs.steampowered.com (valve181.cs.steampowered.com): Closing connection
[2013-09-23 10:36:50] HTTP (CS,28) - valve199.cs.steampowered.com (valve199.cs.steampowered.com): Closing connection
[2013-09-23 10:36:50] HTTP (CS,130) - valve43.cs.steampowered.com (valve43.cs.steampowered.com): Closing connection
[2013-09-23 10:36:50] HTTP (CS,129) - valve42.cs.steampowered.com (valve42.cs.steampowered.com): Closing connection
So yes, it looks like the two bugs are essentially exactly the same problem: Steam is seeing 403 Forbidden errors from the Steam servers when it tries to grab the new manifests.
This was mentioned over in the other issue, but for the record here as well: it looks like at least the India servers can serve up the repo without trouble. I had tried various download locations previously but hadn't left North America, but setting it over to India did the trick for me. Nothing like putting a burden on undersea trunks, yeah?
Closing as this appears to have been resolved. If anyone is still encountering this issue, please open a new issue report.
One of my Linux games, X3: Reunion has been stuck in an "Update Required" status and I've been unable to get it out. I've tried verifying the local game cache, which reports that it's fine. If I try to play the game, I get a "Preparing to launch X3: Reunion" dialog whose progress bar never changes. In the "Downloads" view, it usually starts off in a "Suspended" state - I can hit "pause" and then "resume" which just brings it back into Suspended. The "Resume All" button doesn't seem to do anything. On that screen it says "Updated: 0 bytes / 0 bytes, Time Initiated: 21:20, Time Remaining:" (with no value after Time Remaining) - the "Time Initiated" value might change from run to run, I'm not sure about that.
I've also tried setting it to not auto-update, but that doesn't seem to change it either. This has persisted throughout many restarts of the Steam client over the course of the past week or two. I CAN play the game if I move Steam into offline mode first, at least, so that's nice. It'd be nice to figure out how to get it to start behaving on its own though.
I assume that I could probably fix it by completely deleting the game and then redownloading it, but I'd rather just figure out a way to fix it that's less destructive. There doesn't seem to be any useful output on the console. If there's more information I could provide, please let me know.