Whether this issue occurs in all site collections? Did the navigation cache settings exist before?
Please check the current navigation settings. You have to select Structural Navigation then you can enable and refresh navigation cache.
You could use following PowerShell as administrator to check whether the navigation caching setting is enabled or not. The commend:”Get-SPOStructuralNavigationCacheSiteState” is only check navigation cache state, but we can’t refresh cache by using PowerShell in the SharePoint online.
$AdminSiteURL="https://tenant-admin.sharepoint.com/"
$SiteURL="site collection URL"
$Cred = Get-Credential
Connect-SPOService -URL $AdminSiteURL -Credential $Cred
Get-SPOStructuralNavigationCacheSiteState -SiteUrl $SiteURL
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