MyBB Community Forums

plugins are not working/visible in Task Logs.

but the default Tasks of MyBB is working/visible.

many plugins are affected and not working due to the Task Failure.

I'm not sure what you mean. I add Tasks within my own plugins and haven't noticed any issues.
If you mean that the task simply doesn't add any log entry: that's the fault of the plugin author but it shouldn't affect the functionality.