Apologies for not having provided the console output sooner, and I see that this is already fixed in launcher 1.3.1
For anyone curious, this will not resolve the far less likely situation of the assets folder being overwritten or deleted while the launcher is open (something I've done quite often in personal mod development to "reset" my environment). Symptoms of missing assets on launch are: Missing game icon(s) such as on taskbar, no sounds or music (or a combination depending on what is missing). Closing and re-opening the launcher will properly download the assets in that situation – only wishful thing might be to have a quick check for missing assets/other files on launch, like the check done on load and similar to checking for the existence of the version being launched on clicking "Play", but it's really just an inconvenience that can be remedied by updating your snapshot of the environment.
Pygon
MCL-1712
Apologies for not having provided the console output sooner, and I see that this is already fixed in launcher 1.3.1
For anyone curious, this will not resolve the far less likely situation of the assets folder being overwritten or deleted while the launcher is open (something I've done quite often in personal mod development to "reset" my environment). Symptoms of missing assets on launch are: Missing game icon(s) such as on taskbar, no sounds or music (or a combination depending on what is missing). Closing and re-opening the launcher will properly download the assets in that situation – only wishful thing might be to have a quick check for missing assets/other files on launch, like the check done on load and similar to checking for the existence of the version being launched on clicking "Play", but it's really just an inconvenience that can be remedied by updating your snapshot of the environment.