Couple of things to update you on regarding this issue:

  1. Fresh install of Joplin v3.1.17, same OS - Ubuntu 24.10 - no plugins other than Time Slip, everything worked as expected

  2. When the plugin is using postMessage for iframe communications, there is no note being returned, eg. for updateLogNotes:

{
    "message": {
        "name": "updateLogNotes",
        "notes": []
    }
}