unserialize(): Error at offset 0 after attempting to download and install plugin within control panel Steps to reproduce:


Log into control panel,
Go to Plugin Store tab and install a plugin (in my case hillholliday/craft-user-manual or dolphiq/sitemap),
Plugin installation error screen,
Navigate to /admin and entire site errors out with this message (control panel and frontend)


unserialize(): Error at offset 0 in ProjectConfig.php



Unsuccessful attempts to correct the issue include:


Restoring latest database backup
Restoring backed up composer.json and composer.lock files from storage/composer-backups and running composer install
Clearing storage/runtime/cache


Any suggestions on how to resolve this issue, and insights to why it's happening in the first place?
I think what ended up working was restoring backed up composer.json and composer.lock files, deleting everything in /vendor directory, and then running composer install