Composer no more working

Hi everyone and happy new year,

I got a problem with Composer in a Contao 3.5.30 installation. When I click on it, I got this message :

HTML Code:

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Fatal error: Uncaught exception Error with message Class 'Composer\Factory' not found thrown in system/modules/!composer/src/ClientBackend.php on line 294 #0 system/modules/!composer/src/ClientBackend.php(125): ContaoCommunityAlliance\Contao\Composer\ClientBackend->loadComposer()
#1 system/modules/core/classes/Backend.php(423): ContaoCommunityAlliance\Contao\Composer\ClientBackend->generate()
#2 system/modules/core/controllers/BackendMain.php(131): Contao\Backend->getBackendModule('composer')
#3 contao/main.php(20): Contao\BackendMain->run()
#4 {main}

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Just before, Composer seems not to be working as nothing was updating (or installing) when I clicked on update packages.
And Composer itself displayed as it was to update from version 16 to version 16.??.dev but was never updating.

Thanks for help.