Frontend.async_register_built_in_panel broken or changed in 0.115.0?

I am the creator of the Ihc Viewer custom component:

In version 0.114.x it was working fine, but in version 0.115.0 the panel does not load (A messagebox saying unable to load).

The component use the async_register_built_in_panel to load the panel. Some views are registered with http.register_view and some static files with http.register_static_path. The views and static files are working because i can access these directly.

Anybody that can tell me what has changed in 0.0115.0 , so i can make the panel load again?

After looking further into this I have found that HTML support has been removed for the panels, so now you can only use js modules? The current panel is done using polymer 2, so I assume i have to change that to polymer 3 or LitELement ? (I am not at all a polymer expert)

Another question: I don’t see this change it in the release notes, but i guess these are more for the “regular” user. Are there any list of that kind of development changes - specially when there are breaking changes?

There were warnings in the log that it would be removed from 0.115 i think they started around 0.112

https://github.com/home-assistant/core/blob/dc8bfb76dcb4f8dc3131756ba747b62c58aab76a/homeassistant/components/panel_custom/init.py#L117-L118

just found it was listed as a breaking change in 0.112. https://www.home-assistant.io/blog/2020/07/01/release-112/#breaking-changes (2nd item - panel custom)

I still have a 0.114.4 running and i don’t see it in the log. Maybe because i have loglevel set to “warning”. I did not see it in the 0.112 “bearking changes” (i guess i did not associate the custom panel with the frontend.async_register_built_in_panel function). I will have to read the breaking changes more carefully in the future.

Thanks anyway