Hi, There were enormous behind-the-scenes changes on the BokehJS side for version 3.0 so I want to be up front that it’s likely any custom extension code for 2.x will require a substantial re-write for any 3.x version. It’s possible the issue is somehow just with bokeh build and page setup, but more likely it’s with the extension code itself (or both). However, it’s not really possible to speculate about any actual details with so little information. Here are some resources that may help, or at least help to focus the question on specifics:
But first things first: does the extension code work without being pre-compiled? If not, I’d recommend backing up and going through some of the simple examples above successfully in order to be able to compare and contrast to your current code. It’s definitely important to get the code working not-precompiled as a first step, to tease different concerns apart.
Once the code itself is working uncompiled, then it can be possible to address any issues with (or with using) bokeh build. Pre-compiled models is a very arcane corner of Bokeh, I am only aware of a handful of users. So I would actually suggest that any questions about that (or about porting the old code if there are issues there) to a GitHub development discussion, since the folks who can offer the most help are more likely to see a discussion there, than here.
As always, the #1 thing you can do to help other help you efficiently is to pare your problem down to a complete Minimal Reproducible Example so that they can test things out directly.
Lastly, incidentally, the latest version is 3.2.2 and 3.3 will be out in the next few months. If you have to make a big leap, I’d advise you make the biggest leap possible at one time.