Cannot get position out of spotube with Python bindings, works with CLI (and with software other than spotube)

[ghost]

Here is a MWE that gets the position of the player using the Python introspection library:

#!/usr/bin/env python3
import gi
import sys
import datetime

gi.require_version("Playerctl", "2.0")
from gi.repository import Playerctl, GLib
manager = Playerctl.PlayerManager()

def on_refresh_interval(manager):
    player = manager.props.players[0]
    pos = player.get_position()
    pos = pos/(10**6) # convert in seconds
    pos = str(datetime.timedelta(seconds=pos))
    print(f"[on_refersh_interval] pos={pos}")
    return True

playerobj = None
for player in manager.props.player_names:
    if sys.argv[1] == player.name:
        playerobj = player

if not playerobj:
    raise Exception(f"Player {sys.argv[1]} not found")

print(f"Player={playerobj.name}")
player = Playerctl.Player.new_from_name(playerobj)
manager.manage_player(player)
GLib.timeout_add(1000, on_refresh_interval, manager)

loop = GLib.MainLoop()
loop.run()

It works with Firefox using the Plasma Integration addon (*). Here is an example from a random video:

❯ ./spotube_test plasma-browser-integration
Player=plasma-browser-integration
[on_refersh_interval] pos=0:29:35.791492
[on_refersh_interval] pos=0:29:36.929429
[on_refersh_interval] pos=0:29:37.782034
[on_refersh_interval] pos=0:29:38.927179
[on_refersh_interval] pos=0:29:39.779304

However, it doesn't work with spotube. Here is an example:

❯ ./spotube_test spotube
Player=spotube
[ABRIDGED]/spotube_test:12: Warning: g_variant_get_variant: assertion 'g_variant_is_of_type (value, G_VARIANT_TYPE_VARIANT)' failed
  pos = player.get_position()
[ABRIDGED]/spotube_test:12: Warning: g_variant_get_type: assertion 'value != NULL' failed
  pos = player.get_position()
[ABRIDGED]/spotube_test:12: Warning: g_variant_type_is_subtype_of: assertion 'g_variant_type_check (type)' failed
  pos = player.get_position()
[ABRIDGED]/spotube_test:12: Warning: g_variant_get_int64: assertion 'g_variant_is_of_type (value, G_VARIANT_TYPE_INT64)' failed
  pos = player.get_position()
[ABRIDGED]/spotube_test:12: Warning: g_variant_unref: assertion 'value != NULL' failed
  pos = player.get_position()
[on_refersh_interval] pos=0:00:00
[on_refersh_interval] pos=0:00:00
[on_refersh_interval] pos=0:00:00
[on_refersh_interval] pos=0:00:00
[on_refersh_interval] pos=0:00:00
[on_refersh_interval] pos=0:00:00

Notice that the CLI utility can get the position from spotube without problems.
Here is an example with spotube running:

❯ while true; do playerctl --player spotube position; sleep 1; done;
2161.854478
2162.835829
2163.881221
2164.926477
2165.929178
2166.931851
2167.977129
2168.958499

(*) In theory Firefox has native support for MPRIS, but I find it quite lacking (lack of metadata, etc.)

[ghost]

@acrisci is this a bug?