I tried on my test case to build a WAB app and see the same issue with the title.
One thing to remember about WAB is that it is not up to the same JSAPI vintage with Map Viewer, Instant Apps, and Experience Builder. All those are built upon the latest JSAPI 4.x and can take advantage of capabilities that WAB is unable to leverage.
I'm puzzled as to why an older vintage of WAB supports the pop-up correctly and a more recent one does not. But certainly there have been updates to WAB since 2019.
I am not sure at all if this might help you, but I added the Sea Surface Temperature via its URL using Map Viewer Classic, then created a WAB app using the saved map from Classic. I didn't spend but a few seconds configuring the pop-up, but it looks like the time is being displayed correctly.
I'm not sure how your app will be used, but by adding the Living Atlas layer directly from the URL you would not easily be able to share the app publicly. If for internal use, this might work for you if you spend a bit more time with the pop-up.
The issue with Slider has been logged with the dev team, I expect it to be fixed in the upcoming February update. In the meanwhile, I'd suggest logging an issue with support and they might be able to find other workarounds for your WAB issue, and can also help you track progress on the Slider fix.