I’ve used the timestamp trick successfully when I needed to restore an older config.cfg. But the file would have been different than the one in the cloud, so it’s possible the file needs to be changed as well as have a more recent timestamp. If so, clearing the file should do it:
clc 'C:\Program Files (x86)\Steam\userdata\[SteamID]\362890\remote\cfg\config.cfg'
(Again, replace “[SteamID]” with the appropriate folder. Also make sure you include the single quotes around the file path.)
You could also just open the “config.cfg” file in Notepad, edit it or clear out all its contents, and save.
I can’t really say, but if the problem is caused by some corrupt or incorrect data in the Steam Cloud, then you should in theory be able to fix it by disabling the Steam Cloud synchronization for Black Mesa:
Right click on Black Mesa in the Steam Library and click Properties. Then select the Updates tab and uncheck the “Enable Steam Cloud synchronization for Black Mesa”. Restart Steam.
Then try the other suggestions again. (Alternatively, completely uninstall Black Mesa, delete any leftover files/folders in “***\steamapps\common\Black Mesa” and reinstall. Then verify the cache once.)
One of the suggestions was to delete sound.cache from the “Black Mesa\bms\sound” folder, but for good measure make sure you delete all the .cache files in the “Black Mesa\bms”, “Black Mesa\bms\sound”, “Black Mesa\hl2” and “Black Mesa\hl2\sound” folders. Also delete “config.cfg” (and userconfig.cfg if it exists) in the “Black Mesa\bms\cfg” folder, and the savegames in "**\steamapps\common\Black Mesa\bms\save".
Another thing you could try is to launch the game once with the [tt]-autoconfig[/tt] launch option.
If disabling Steam Cloud synchronization and cleaning up / reinstalling Black Mesa doesn’t resolve the problem, then there must be something else going on, and I’m not sure what else to suggest.