The seccomp tools are dynamically linked:

$ file /usr/lib/snapd/snap-seccomp /snap/core/current/usr/lib/snapd/snap-seccomp
/usr/lib/snapd/snap-seccomp:                   ELF 64-bit MSB executable, IBM S/390, version 1 (SYSV), dynamically linked, interpreter /lib/ld64.so.1, BuildID[sha1]=ac22cf91f26d3e3f32132a8f717a22af7caf49fc, for GNU/Linux 3.2.0, stripped
/snap/core/current/usr/lib/snapd/snap-seccomp: ELF 64-bit MSB executable, IBM S/390, version 1 (SYSV), dynamically linked, interpreter /lib/ld64.so.1, for GNU/Linux 3.2.0, Go BuildID=wD-y12JBR_fQqHU08D57/n6hBHyUsBFuJ5Czn6fF7/JXIu77JtC7eIGO4BPOpW/1cKteqVwlvsiXC73WA1t, BuildID[sha1]=ed5cbba6dba5be3b12f065fca9981725da2c75cc, stripped


As for updates, there were apt updates, followed by reloads (probably the configure step).
That eventually restarted the snap daemon it seems.

Apr 15 08:43:50 s1lp05 systemd[1]: Stopped Daily apt download activities.
Apr 15 08:43:50 s1lp05 systemd[1]: Stopping Daily apt download activities.
Apr 15 08:43:50 s1lp05 systemd[1]: Started Daily apt download activities.
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:52 s1lp05 systemd[1]: Reloading.
Apr 15 08:43:52 s1lp05 systemd[1]: /lib/systemd/system/dbus.socket:5: ListenStream= references a path below legacy directory /var/run/, updating /var/run/dbus/system_bus_socket → /run/dbus/>
Apr 15 08:43:52 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:53 s1lp05 dbus-daemon[3425]: [system] Reloaded configuration
Apr 15 08:43:57 s1lp05 systemd[1]: Stopping Snap Daemon...
Apr 15 08:43:57 s1lp05 snapd[2423936]: main.go:155: Exiting on terminated signal.
Apr 15 08:43:57 s1lp05 systemd[1]: snapd.service: Succeeded.
Apr 15 08:43:57 s1lp05 systemd[1]: Stopped Snap Daemon.
Apr 15 08:43:57 s1lp05 systemd[1]: snapd.socket: Succeeded.
Apr 15 08:43:57 s1lp05 systemd[1]: Closed Socket activation for snappy daemon.


That was per /var/log/dpkg.log
2020-04-15 08:43:57 upgrade snapd:s390x 2.44+20.04 2.44.3+20.04

Core was refreshed on 1st of April I think:
ubuntu@s1lp05:~$ snap info core
...
refresh-date: 20 days ago, at 18:14 EDT
channels:
  latest/stable:    16-2.44.1                 2020-03-31 (8932) 89MB -
  latest/candidate: 16-2.44.3                 2020-04-14 (9064) 89MB -
  latest/beta:      16-2.44.3                 2020-04-10 (9064) 89MB -
  latest/edge:      16-2.44.3+git1757.66c7369 2020-04-20 (9125) 92MB -
installed:          16-2.44.1                            (8932) 89MB core
ubuntu@s1lp05:~$ date
Mon Apr 20 10:36:24 EDT 2020

TL;DR:
- snapd restart 24 march
- core update 1st of April
- snapd upgrade and restart 15 April
=> here the key got regenerated