FYI I don't think this is related to the Preview issue I was seeing but I did receive the following error when starting up 0.29 the first time:

{
  "ctx": "h:run",
  "err": {
    "status": "unknown",
    "msg": "",
    "payload": "{\"msg\":\"Unexpected token \\\"\",\"stack\":\"SyntaxError: Unexpected token \\\"\\n\\tat B (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:357:25016)\\n\\tat G (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:357:25383)\\n\\tat /home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:357:25898\\n\\tat Q (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:357:26060)\\n\\tat Object.parse (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:357:26485)\\n\\tat Object.t.readJSONWithComments (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:78:10104)\\n\\tat async Function.upgradeOrCreate (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:129:11450)\\n\\tat async Function.update (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:129:10394)\\n\\tat async h.execute (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:661:53429)\\n\\tat async h.run (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:9:102919)\\n\\tat async /home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:9:78209\\n\\tat async /home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:286:92406\\n\\tat async k (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:286:91757)\\n\\tat async S (/home/archfae/.vscode-oss/extensions/dendron.dendron-0.29.0/dist/extension.js:286:95956)\"}"
  }
}

Seems like it only occurred during the initial startup since the upgrade though; subsequent startups don't show that error.