Update fails - plugin is at the latest version

Can not update any plugins from WPMUDEV Dashboard plugin. It shows "The plugin is at the latest version"
There are some errors in the debug.log file like
WPMUDEV API Error] 4.5.2 | cURL error 28: Operation timed out after 15002 milliseconds with 0 bytes received ((unknown URL) [500])
the max_execution_time is set to 2000 and curl is configured to access wpmudev dashboard api
I have cleared all caching files and also deactivated white label plugins but not helps