Weblistbox 2.0 - puzzling behavior. Insights anyone?

I have this problem with weblistboxes in Web 2.0: in some cases, especially where I have containers, the listboxes just won’t render correctly on screen. Yet, the data is there. Hitting inspection on the browser instantly shows the listbox, which then works almost normally. I cannot reproduce this in a simple program, nor on simple pages in the same program. As you know, no demo program, no feedback… In simpler layouts, issuing a UpdateBrowser command after filling the listbox is sufficient. Not here. This page has several containers, that become visible through segmentedbuttons. container. that manages different kinds of texts related to the customer.

I am completely stumped by this behavior. This screen works perfectly in 2019 R3.1.! Any insights would be welcome.

I would welcome any possible suggestions to figure out what is going on.

It could be related to one of these:

Thank you @David_Cox,

It looks a lot like FR 62823. Interesting that I did not find these two reports when I scanned Feedback. I confirm that I have the issue with containers, pagepanels and tabpanels.

I suppose that I can only wait for a later release. Hopefully, nothing will happen in the mean time to break my 2019 R3.1 application. This is something that should be a high priority fix. We cannot create real life applications of any level of complexity without containers or panels.