This issue went away for me after I restarted the Steam client.

When I export PULSE_SERVER=/dev/null, the steam client starts successfully.

After the latest update, I got that thing too. Beta and non-beta; so it might be related to a system update. System is Debian Sid. Setting PULSE_SERVER=/dev/null doesn't help, and gdb output is pretty inconclusive:

Fri May 15 2020 08:35:16.963210 - steam 1.12.2 startup with PID=240313, config=/home/user/.local/share/Steam/config, runtime=/opt/Games/Steam/SteamApps/common/SteamVR
Fri May 15 2020 08:35:16.963260 - vrclient type=VRApplication_SteamWatchdog
/data/src/common/pipes.cpp (770) : Assertion Failed: fatal stalled cross-thread pipe
/data/src/common/pipes.cpp (770) : Assertion Failed: fatal stalled cross-thread pipe
--Type for more, q to quit, c to continue without paging--
continue without paging--
Thread 1 "steam" received signal SIGTRAP, Trace/breakpoint trap.
0xed75f5fd in ?? () from /home/user/.local/share/Steam/ubuntu12_32/steamclient.so
(gdb)
(gdb) bt
#0 0xed75f5fd in () at /home/user/.local/share/Steam/ubuntu12_32/steamclient.so
#1 0xed75f8c9 in () at /home/user/.local/share/Steam/ubuntu12_32/steamclient.so
#2 0xed750fa8 in () at /home/user/.local/share/Steam/ubuntu12_32/steamclient.so
#3 0xed381d9e in () at /home/user/.local/share/Steam/ubuntu12_32/steamclient.so
#4 0xf2b8ab0f in () at /home/user/.local/share/Steam/ubuntu12_32/steamui.so
#5 0xf2b7775a in () at /home/user/.local/share/Steam/ubuntu12_32/steamui.so
#6 0xf2ab8d74 in () at /home/user/.local/share/Steam/ubuntu12_32/steamui.so
#7 0x56590c60 in RunSteam(int, char**, bool) ()
#8 0x56591be3 in ()
#9 0x565799ac in ()
#10 0xf79b4ef1 in __libc_start_main () at /lib/i386-linux-gnu/libc.so.6
#11 0x5657e0b9 in _start ()

I now deleted SteamVR; but the picture remains the same.

Might this have something to do with the upgrade of libc6:i386 on May 11? because that would fit the time frame: https://metadata.ftp-master.debian.org/changelogs//main/g/glibc/glibc_2.30-8_changelog

It happened to me on Ubuntu 21.10. You might want to change that label

This suddenly started happening to me, too, also on Gentoo, oddly enough, opted in to the Steam client beta. I've been updating my system a lot lately so would think it is a system update except, well, the issue started in 2018, and I certainly did not have this issue back in 2018.

Suddenly started to happen to me on ubuntu 22.04.
Running "PULSE_SERVER=/dev/null steam" solves problem with launching steam, but removes sound from games.

The problem still exists. This is from Oxygen Not Included, unity Player.log

src/common/pipes.cpp (883) : fatal stalled cross-thread pipe.
/data/src/common/pipes.cpp 883 fatal stalled cross-thread pipe.Caught fatal signal - signo:5 code:128 errno:0 addr:(nil)
Obtained 34 stack frames.
#0  0x007f3a1a8c8f9d in Breakpad_SteamWriteMiniDumpUsingExceptionInfoWithBuildId
#1  0x007f3a1a751a9e in Steam_ReleaseThreadLocalMemory
#2  0x007f3bc0157bb6 in SteamAPI_Init
#3  0x000000404e74a7 in (wrapper managed-to-native) Steamworks.NativeMethods:SteamAPI_Init ()

Actually fixed all problems with steam (there was not only sound issues for me, but oom-killer and shader issues, too).

The source of problems was that I had an invalid config in /etc/security/limits.conf file:

* soft stack 1048576
* hard stack 1048576

This sets default stack size for threads to 1Gb (so, for 32-bit environment like steam, you could only have 4 threads with default stack size).

Don't know when I added this two lines to config, but after removing them, everything is working again.

The source of problems was that I had an invalid config in /etc/security/limits.conf file:

* soft stack 1048576
* hard stack 1048576

What's your distro? /etc/security/limits.conf should not work anymore, the limits should be in /etc/systemd/user.conf and /etc/systemd/system.conf nowawayds, odd.
Also, it's unusual for a limit that's "too high" prevent things from running correctly, it's usually the ones that are too low that have this effect.

Distro is ubuntu 22.04

/etc/security/limits.conf works as usual (and file exists).

Also, it's unusual for a limit that's "too high" prevent things from running correctly, it's usually the ones that are too low that have this effect.

Yep, but with 32-bit applications like steam with only 4Gb ram available it is possible :)

I understand this issue might be caused by some specific distro configuration?

I use Steam Flatpak on Debian 12.1.0 and it crashes during game downloads. It causes my Steam client window to stop responding and then my Gnome Wayland session freezes. Since I didn't experience this issue with Steam Flatpak on other distros, I now suspect this might be caused by some configuration in Debian.