Packaging a project to HTML5 while Online Framework is enabled seems to cause packaging failures. It produces the following errors from the Output Log:
PackagingResults: Error: unresolved symbol: _Z5HtoNSt
PackagingResults: Error: unresolved symbol: _Z5NtoHSt
PackagingResults: Error: unresolved symbol: _Z5HtoNLj
PackagingResults: Error: UBT ERROR: Failed to produce item: E:\Epic\Unreal Projects\HTML5FailBuild\Binaries\HTML5\HTML5FailBuild.js
PackagingResults: Error: UnrealBuildTool failed. See log for more details. (C:\Users\daniel.hamilton\AppData\Roaming\Unreal Engine\AutomationTool\Logs\E+Epic+UE_4.21\UBT-HTML5FailBuild-HTML5-Development.txt)
PackagingResults: Error: Unknown Error
Tested in 4.20.3 (CL - 4369336), 4.21.1 (CL - 4571667), 4.22 (CL - 4572453)
Expected: The engine packages the project with no difficulties
Result: The Output Log displays multiple errors
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-66695 in the post.