Full Snapshot UI timeout and size change every time I launch it

When I launch a full snapshot of my RPi3B, the UI displays a ‘504 Gateway Time-out’ error…
Please take a look at the hardcopy:


and at the logs:

20-10-18 15:45:49 INFO (MainThread) [supervisor.api.snapshots] Download snapshot d9f9c8b2
20-10-18 15:47:26 INFO (MainThread) [supervisor.snapshots] Found 1 snapshot files
20-10-18 15:48:12 INFO (MainThread) [supervisor.snapshots] Full-Snapshot 61e99f2e start
20-10-18 15:48:12 INFO (MainThread) [supervisor.snapshots] Snapshot 61e99f2e store Add-ons
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on core_ssh
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon core_ssh
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on core_samba
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon core_samba
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_appdaemon
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_appdaemon
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on core_configurator
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon core_configurator
20-10-18 15:48:12 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_vscode
20-10-18 15:48:13 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_vscode
20-10-18 15:48:13 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_influxdb
20-10-18 15:48:46 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_influxdb
20-10-18 15:48:46 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_grafana
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_grafana
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on core_mosquitto
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon core_mosquitto
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_glances
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_glances
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on a0d7b954_ssh
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon a0d7b954_ssh
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Build snapshot for add-on core_nginx_proxy
20-10-18 15:48:47 INFO (MainThread) [supervisor.addons.addon] Finish snapshot for addon core_nginx_proxy
20-10-18 15:48:47 INFO (MainThread) [supervisor.snapshots] Snapshot 61e99f2e store folders
20-10-18 15:48:47 INFO (SyncWorker_4) [supervisor.snapshots.snapshot] Snapshot folder homeassistant
20-10-18 15:50:45 INFO (MainThread) [supervisor.snapshots] Found 1 snapshot files
20-10-18 15:50:54 INFO (MainThread) [supervisor.snapshots] Found 1 snapshot files
20-10-18 15:51:04 INFO (SyncWorker_4) [supervisor.snapshots.snapshot] Snapshot folder homeassistant done
20-10-18 15:51:04 INFO (SyncWorker_7) [supervisor.snapshots.snapshot] Snapshot folder share
20-10-18 15:51:05 INFO (SyncWorker_7) [supervisor.snapshots.snapshot] Snapshot folder share done
20-10-18 15:51:05 INFO (SyncWorker_0) [supervisor.snapshots.snapshot] Snapshot folder ssl
20-10-18 15:51:05 INFO (SyncWorker_0) [supervisor.snapshots.snapshot] Snapshot folder ssl done
20-10-18 15:51:05 INFO (SyncWorker_3) [supervisor.snapshots.snapshot] Snapshot folder media
20-10-18 15:51:05 INFO (SyncWorker_3) [supervisor.snapshots.snapshot] Snapshot folder media done
20-10-18 15:51:05 INFO (SyncWorker_6) [supervisor.snapshots.snapshot] Snapshot folder addons/local
20-10-18 15:51:05 INFO (SyncWorker_6) [supervisor.snapshots.snapshot] Snapshot folder addons/local done
20-10-18 15:51:12 INFO (MainThread) [supervisor.snapshots] Full-Snapshot 61e99f2e done

But what is worrying me is none of the same snapshot I did has the same size…
image

What goes wrong? Me? My RPi? My SSD? The snapshot script/routine?

Thank you for your time.

Olivier