Here is a relevant log fragment of snapd, with DEBUG turned on:
Feb 19 01:39:49 nyks snapd[4148]: store_action.go:541: DEBUG: Deltas enabled. Adding header Snap-Accept-Delta-Format: xdelta3
Feb 19 01:39:49 nyks snapd[4148]: retry.go:50: DEBUG: Retrying https://api.snapcraft.io/v2/snaps/refresh, attempt 1, elapsed time=4.112µs
Feb 19 01:39:49 nyks snapd[4148]: store.go:785: DEBUG: cannot set device session: no device serial yet
Feb 19 01:39:49 nyks snapd[4148]: retry.go:62: DEBUG: The retry loop for https://api.snapcraft.io/v2/snaps/refresh finished after 1 retries, elapsed time=287.533185ms, status: 200
Feb 19 01:39:49 nyks snapd[4148]: store_action.go:541: DEBUG: Deltas enabled. Adding header Snap-Accept-Delta-Format: xdelta3
Feb 19 01:39:49 nyks snapd[4148]: retry.go:50: DEBUG: Retrying https://api.snapcraft.io/v2/snaps/refresh, attempt 1, elapsed time=3.006µs
Feb 19 01:39:49 nyks snapd[4148]: store.go:785: DEBUG: cannot set device session: no device serial yet
Feb 19 01:39:54 nyks snapd[4148]: retry.go:180: DEBUG: Retrying because of: EOF (EOF)
Feb 19 01:39:54 nyks snapd[4148]: retry.go:113: DEBUG: ShouldRetryError: EOF *errors.errorString -> true
Feb 19 01:39:54 nyks snapd[4148]: retry.go:50: DEBUG: Retrying https://api.snapcraft.io/v2/snaps/refresh, attempt 2, elapsed time=5.001999817s
Feb 19 01:39:54 nyks snapd[4148]: store.go:785: DEBUG: cannot set device session: no device serial yet
Feb 19 01:39:59 nyks snapd[4148]: retry.go:62: DEBUG: The retry loop for https://api.snapcraft.io/v2/snaps/refresh finished after 2 retries, elapsed time=10.265259231s, status: 408
Feb 19 01:39:59 nyks snapd[4148]: daemon.go:217: DEBUG: pid=109370;uid=0;socket=/run/snapd.socket; POST /v2/snaps 10.558063781s 400