Intermittent mount error installing snaps from within unprivileged lxc container

I’m trying to install a snap from inside my unprivileged container, but I run into a mount error. I’ve seen similar errors across different snaps, so I assume something is borked with my environment. There appears to be some kind of automatic bug filing (OOPSID) but I don’t know where to track it. Here’s an example of the error:

$ sudo snap install standard-notes
error: cannot perform the following tasks:
- Mount snap "core18" (2246) (systemctl command [start snap-core18-2246.mount] failed with exit status 1: Job failed. See "journalctl -xe" for details.
)

journalctl

Nov 15 04:32:49 standard-notes sudo[413]:   ubuntu : TTY=pts/1 ; PWD=/home/ubuntu ; USER=root ; COMMAND=/usr/bin/snap install standard-notes
Nov 15 04:32:49 standard-notes sudo[413]: pam_unix(sudo:session): session opened for user root by (uid=0)
Nov 15 04:32:49 standard-notes snapd[199]: api_snaps.go:303: Installing snap "standard-notes" revision unset
Nov 15 04:32:53 standard-notes systemd[1]: Reloading.
Nov 15 04:32:53 standard-notes systemd[1]: systemd-logind.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-logind.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-journald.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-journald.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-udevd.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-udevd.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: Reloading.
Nov 15 04:32:53 standard-notes systemd[1]: systemd-logind.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-logind.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-journald.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-journald.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-udevd.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-udevd.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: Mounting Mount unit for core18, revision 2246...
-- Subject: A start job for unit snap-core18-2246.mount has begun execution
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- A start job for unit snap-core18-2246.mount has begun execution.
-- 
-- The job identifier is 378.
Nov 15 04:32:53 standard-notes systemd[607]: snap-core18-2246.mount: Failed to link user keyring into session keyring: Required key not available
Nov 15 04:32:53 standard-notes systemd[607]: snap-core18-2246.mount: Failed to set up kernel keyring: Required key not available
Nov 15 04:32:53 standard-notes systemd[607]: snap-core18-2246.mount: Failed at step KEYRING spawning /bin/mount: Required key not available
-- Subject: Process /bin/mount could not be executed
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- The process /bin/mount could not be executed and failed.
-- 
-- The error number returned by this process is ERRNO.
Nov 15 04:32:53 standard-notes systemd[1]: snap-core18-2246.mount: Mount process exited, code=exited, status=237/KEYRING
-- Subject: Unit process exited
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- An n/a= process belonging to unit snap-core18-2246.mount has exited.
-- 
-- The process' exit code is 'exited' and its exit status is 237.
Nov 15 04:32:53 standard-notes systemd[1]: snap-core18-2246.mount: Failed with result 'exit-code'.
-- Subject: Unit failed
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- The unit snap-core18-2246.mount has entered the 'failed' state with result 'exit-code'.
Nov 15 04:32:53 standard-notes systemd[1]: Failed to mount Mount unit for core18, revision 2246.
-- Subject: A start job for unit snap-core18-2246.mount has failed
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- A start job for unit snap-core18-2246.mount has finished with a failure.
-- 
-- The job identifier is 378 and the job result is failed.
Nov 15 04:32:53 standard-notes systemd[1]: snapd.service: Got notification message from PID 606, but reception only permitted for main PID 199
Nov 15 04:32:53 standard-notes systemd[1]: Reloading.
Nov 15 04:32:53 standard-notes systemd[1]: systemd-logind.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-logind.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-journald.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-journald.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-udevd.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-udevd.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: Reloading.
Nov 15 04:32:53 standard-notes systemd[1]: systemd-logind.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-logind.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-journald.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-journald.service failed: Invalid argument
Nov 15 04:32:53 standard-notes systemd[1]: systemd-udevd.service: Attaching egress BPF program to cgroup /sys/fs/cgroup/unified/system.slice/systemd-udevd.service failed: Invalid argument
Nov 15 04:32:53 standard-notes snapd[199]: taskrunner.go:271: [change 5 "Mount snap \"core18\" (2246)" task] failed: systemctl command [start snap-core18-2246.mount] failed with exit status 1: Job failed. See "journalctl -xe" for details.
Nov 15 04:32:53 standard-notes systemd[1]: Cannot find unit for notify message of PID 667, ignoring.
Nov 15 04:32:56 standard-notes snapd[199]: handlers.go:512: Reported install problem for "core18" as 19d5bf50-45cd-11ec-b098-fa163e102db1 OOPSID
Nov 15 04:32:56 standard-notes sudo[413]: pam_unix(sudo:session): session closed for user root

Container:

$ snap version
snap    2.52.1
snapd   2.52.1
series  16
ubuntu  20.04
kernel  5.11.0-40-generic

Host:

$ snap list lxd
Name  Version  Rev    Tracking       Publisher   Notes
lxd   4.20     21858  latest/stable  canonical✓  -

Looks like an AppArmor denial

[15741.190668] audit: type=1400 audit(1637635268.513:3539): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxd-standard-notes_</var/snap/lxd/common/lxd>" name="/run/systemd/unit-root/var/cache/private/fwupdmgr/" pid=70507 comm="(fwupdmgr)" flags="rw, nosuid, remount, bind"