Okay, so when this happens I got seb128 to run:

  gdbus call --session --dest com.canonical.Unity.Panel.Service --object-path /com/canonical/Unity/Panel/Service --method com.canonical.Unity.Panel.Service.Sync

and it returned this:

  ([('libappmenu.so', '0xa048950', '', '_Fichier', true, true, uint32 0, '', false, false, 0), ('libappmenu.so', '0xa04caa8', '', 'É_dition', true, true, 0, '', false, false, 1), ('libappmenu.so', '0xae926c78', '', '_Affichage', true, true, 0, '', false, false, 2), ('libappmenu.so', '0xae939310', '', '_Rechercher', true, true, 0, '', false, false, 3), ('libappmenu.so', '0xae929308', '', '_Terminal', true, true, 0, '', false, false, 4), ('libappmenu.so', '0x9ecbb48', '', '_Onglets', true, false, 0, '', false, false, 5), ('libappmenu.so', '0xa04d1b8', '', 'Aid_e', true, true, 0, '', false, false, 6), ('libapplication.so', '0x9fff500', 'indicator-weather', '15 ˚C', true, true, 1, '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', true, true, 50), ('libapplication.so', '0x9fe6e18', 'tomboy-notes', '', false, false, 1, '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', true, true, 51), ('libapplication.so', '0xa017f80', 'bluetooth-manager', '', false, false, 1, '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', true, true, 250), ('libapplication.so', '0xa004100', 'nm-applet', '', false, false, 1, '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', true, true, 400), ('libmessaging.so', '0x9dfcaac', '', '', false, false, 1, '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', true, true, 150), ('libpower.so', '0x9e67654', '', '(chargé)', true, false, 6, '. GThemedIcon battery-full-charged-symbolic battery-full-charging-symbolic gpm-battery-full gpm-battery-100 battery-full-charged battery-full-charging ', true, true, 200), ('libsoundmenu.so', '0x9eec084', '', '', false, false, 1, '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', true, true, 450), ('libdatetime.so', '0xb692681c', '', 'jeu. 22 sept. 17:26', true, true, 0, '', false, false, 500), ('libsession.so', '0x9eb4034', '', 'seb128', true, true, 1, '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', true, true, 550), ('libsession.so', '0x9eb4058', '', '', false, false, 1, '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', true, false, 551)],)

Which includes the session icon.  So that makes me think this isn't an indicator-session issue.