Issues with processing updates can be caused by various reasons. In most cases, that would be server-side problems, but there are other factors too.
System requirements not met
To process updates in bulk, your MainWP Dashboard needs enough time and available memory.
To improve your MainWP performance, try to increase the following values:
PHP Memory Limit
WordPress Memory Limit
PHP Max Execution Time
cURL Timeout
It would be best to make these updates to both sides, MainWP Dashboard and the child site(s) in the issue. If you are running your MainWP Dashboard on a shared hosting environment, please read this post.
Conflicts with other plugins
In some cases, there are 3rd party plugins that can cause problems with processing updates. In most cases, these are Security and Caching plugins. If your MainWP setup meets all system requirements but updates are still not processed as expected, please try to deactivate 3rd party plugins on a child site in the issue temporarily and see if that helps.
Fine-tune your MainWP setup
If none of the above doesn’t help, try to readjust the MainWP Advanced Setting (MainWP > Settings > Advanced Options).
Lower the number of Maximum Simultaneous Requests
Lower the number of Maximum Simultaneous Update Requests
Increase the Minimal Delays Between Requests
Repeat this process until you find the sweet spot for your setup.
If this also doesn’t help, feel free to open a helpdesk ticket so the MainWP Dev team can investigate this further.
If updates are failing only for Premium plugins, ensure that items in issue have valid license keys and are properly activated. Also, please check this help document.