OS: MacOS X 10.12.6
The attached file is a demo I created that uses Mozilla's PDF.js framework to display a PDF from a container field in a web viewer. (This technique sidesteps several major technical limitations of FM's interactive container type.)
Steps to replicate:
1.) Open the attached file in FileMaker 16 or earlier on OS X 12.6. As the web viewer draws, dismiss the successive alerts that come up. After all alerts are done (roughly 12-15 alerts), the sample PDF displays in the web viewer. Then you can close the file.
2.) Open the attached file in FileMaker 17 Advanced on OS X 12.6.
Same as described for FMA 16 in #1 above.
Actual behavior in FM 17:
5.) Make a simple edit to the field "jsscripts", say by adding a whitespace to a comment line, and exit the record to refresh the web viewer.
8.) Now, enter layout mode by hitting CMD-L.
9.) Immediately re-enter browse mode by hitting CMD-B.
10.) Now, the Alerts complete all the way to the end of the series, and the PDF displays in the web viewer as expected.
11.) From here on in, the web viewer will update properly and behave as expected, until you close the file.
EDIT, 10/17: I just tried using a Set Web Viewer script step to get the Web Viewer to manually update. I tried all three available options: reset, reload, and Go To Url with the proper data url. None of these work if you have not left end re-entered Browse mode yet. They all work afterwards. Same for Refresh Object.