Getting a JavaScript error in the browser console, looking to understand

I’ve fired up a local instance of Gramps Web to play around with. Initial setup seemed fine, and when I Iog in as the owner I get the page showing “Get started - To start building your family tree, add yourself as a person or import a family tree file”. All well and good, but there are numerous warnings and errors in the browser console
.
The warnings are:

Lit is in dev mode. Not recommended for production! See https://lit.dev/msg/dev-mode for more information. reactive-element.ts:76:15
Multiple versions of Lit loaded. Loading multiple versions is not recommended. See https://lit.dev/msg/multiple-versions for more information. reactive-element.ts:76:15
Element gramps-js scheduled an update (generally because a property was set) after an update completed, causing a new update to be scheduled. This is inefficient and should be avoided unless the next update can only be scheduled as a side effect of the previous update. See https://lit.dev/msg/change-in-update for more information. reactive-element.ts:92:15
Element grampsjs-list-item scheduled an update (generally because a property was set) after an update completed, causing a new update to be scheduled. This is inefficient and should be avoided unless the next update can only be scheduled as a side effect of the previous update. See https://lit.dev/msg/change-in-update for more information. reactive-element.ts:76:15
Element grampsjs-tooltip scheduled an update (generally because a property was set) after an update completed, causing a new update to be scheduled. This is inefficient and should be avoided unless the next update can only be scheduled as a side effect of the previous update. See https://lit.dev/msg/change-in-update for more information. reactive-element.ts:92:15
Element grampsjs-view-dashboard scheduled an update (generally because a property was set) after an update completed, causing a new update to be scheduled. This is inefficient and should be avoided unless the next update can only be scheduled as a side effect of the previous update. See https://lit.dev/msg/change-in-update for more information. reactive-element.ts:92:15

And then the error, which is reported twice in the console.

Uncaught (in promise) TypeError: IntersectionObserver constructor: 'new' is required
    firstUpdated GrampsjsConnectedComponent.js:157

I haven’t printed the entire traceback, but can if it’s deemed necessary.
Should I worry about this error? I’m using front-end code that hasn’t been minified by Rollup; is this a reasonable setup to work with to ease learning my way around the code, debugging etc?

What could be the reason for the error?

Also note that I can use the UI to select a file to import, but then the import fails immediately - I haven’t investigated that yet, though.

As I’m effectively using a repo checkout, here’s what I get from “System Information”.

Gramps 6.0.6
Gramps Web API 3.7.0
Gramps Web Frontend [VI]{version}[/VI]
Gramps QL 0.4.0
Sifts 1.1.1
locale: en_GB
multi-tree: false
task queue: true
OCR: false
chat: false

Please check Github for existing issues, thanks!

Whoops, sorry for the noise, will check in future!

I applied the changes in PR#915, and then tried doing an import. It failed: in the browser console I see

Error: appState is null for element
<grampsjs-task-progress-indicator id="progress-tree" class="button" taskname="importFile" size="20" hideafter="0" pollinterval="0.2" open="">```

I checked the Celery log, and it didn’t report any import errors:

[2026-01-20 16:44:55,464: INFO/MainProcess] Task gramps_webapi.api.tasks.import_file[e7715ced-bde7-4279-86d5-93fb8d3bb1e1] received
[2026-01-20 16:44:56,488: INFO/ForkPoolWorker-2] Task gramps_webapi.api.tasks.import_file[e7715ced-bde7-4279-86d5-93fb8d3bb1e1] succeeded in 1.022929151004064s: None

I don’t see any analogous issues in the bug tracker. The file to import has only a small tree (< 500 people). And it seems to have succeeded - the records seem to have been imported. Refreshing the page shows this. (I initially thought it failed because of the error in the console and the red cross that appeared.)