Can you give me (super) admin and (s)ftp access so I can take a look?
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I saw no errors on your site. Not on the frontend or in the administrator.
I installed the latest version of Sourcerer on your site. It took quite long to install, but finished without errors.
All seems fine.
Joomla 4 uses namespaces, which get loaded through a ps4 namespace generated file (which is in your cache folder).
If you get that error, it seems like that file is not getting generated in time for the rest of the page to render.
Seeing how extremely long it took your server to install that latest version of Sourcerer I installed, I would guess the issue is on your server.
Either something weird and slow on the file server or something in your database.