This bug has been around for about two months, ever since the beta version of the new market was released. It happens every day at the same time, and it fixes itself several hours later at the same time every day. The last week it's been happening more frequently and even locks your own inventory; you can only see your friends'. It seems to happen to everyone at the same time. On the other hand, the first day of the market crash was the only day it didn't happen. We can only hope that Valve listens to us and fixes it someday...

Wow... so we’re all just stuck waiting every day for it to “fix itself”? 😭
Valve really needs to step up and look into this, it’s been months already!

The problem here is this zero communication policy when Valve changes or adjusts mechanics.

I've been struggling with this myself for months (more than two) because I read profile data from Steam for my website via Steam WebAPI. The good thing about it? I had to get to deal with several mechanics. Cache, cron jobs, query types, adjusting the scripts and performance multiple times. At first, I thought it was a mistake on my part (for example, sloppy code), but then more and more posts started appearing in the forums. In situations like this, the only thing to do is wait and see and react accordingly... if possible.

And from the feedback in the main forum, just a small group is using the API. There are a few posts about this (e.g. rate limit adjustments), but nothing official.

You hit an API quota limit. This quota limit is IPv4 based.

First, try clearing the web cache of the Steam client to see if it is just a cached page issue.

If that doesn't help, restart your router, this should give you a new IPv4 address.

If restarting your router doesn't help, you'll have to wait it out.

If you waited several days to weeks, your only recourse is getting a public IPv4 address. It doesn't matter whether this one is static or dynamic. Ask your ISP on how to obtain one.

Reason:
IPv4 addresses are not unique anymore. As there are more humans (8 billion) than IPv4 addresses (4.2 billion), ISPs have chosen to route users together on an identical IPv4 address. This technique is known as CGNAT.[en.wikipedia.org]
For Valve's inventory and community market API this bundled together group of users using CGNAT or Dual Stack Lite looks like a single user.

Workaround if you are behind Dual Stack Lite:
If you are behind Dual Stack Lite (shared IPv4 address, dedicated IPv6 prefix), temporarily disable IPv4 on your system after you made sure IPv6 support is enabled in your router to force Steam to use IPv6. Undo this step after you finished using the market or inventory (you will have to redo it every time you use either). Do not use this as a permanent solution because not every service on the internet did implement IPv6 support yet.

If you already have a public also known as dedicated IPv4 address, you should stop spamming inventory actions.

Originally posted by Ettanin:

You hit an API quota limit. This quota limit is IPv4 based.

First, try clearing the web cache of the Steam client to see if it is just a cached page issue.

If that doesn't help, restart your router, this should give you a new IPv4 address.

If restarting your router doesn't help, you'll have to wait it out.

If you waited several days to weeks, your only recourse is getting a public IPv4 address. It doesn't matter whether this one is static or dynamic. Ask your ISP on how to obtain one.

Reason:
IPv4 addresses are not unique anymore. As there are more humans (8 billion) than IPv4 addresses (4.2 billion), ISPs have chosen to route users together on an identical IPv4 address. This technique is known as CGNAT.[en.wikipedia.org]
For Valve's inventory and community market API this bundled together group of users using CGNAT or Dual Stack Lite looks like a single user.

Workaround if you are behind Dual Stack Lite:
If you are behind Dual Stack Lite (shared IPv4 address, dedicated IPv6 prefix), temporarily disable IPv4 on your system after you made sure IPv6 support is enabled in your router to force Steam to use IPv6. Undo this step after you finished using the market or inventory (you will have to redo it every time you use either). Do not use this as a permanent solution because not every service on the internet did implement IPv6 support yet.

If you already have a public also known as dedicated IPv4 address, you should stop spamming inventory actions.

As i said, nothing official.

The technical recommendation to temporarily enforce IPv6 may be functionally correct but IPv6 continues to pose a security risk when it comes to logging and tracking by ISPs, and configuration/policies are also an issue.

So weakening network security/enviroment is really great advice. Are you guys out of your minds with the advice that is carelessly spread here via copy/paste?

Furthermore, it is not the job of the common home users to "fix" something, when a platform like Steam fails here and their owner doesn't even communicate properly.

If you already have a public also known as dedicated IPv4 address, you should stop spamming inventory actions.

This statement is fundamentally incorrect for the majority of users.