Nuget restore task taking an excessive length of time

Hi

We have DevOps pipelines being run on self-hosted build servers, building a large solution (~50 projects, currently a mix of full framework and NetStandard) with a lot of nugets being referenced. Unfortunately the codebase is far too large to be pulled onto the standard azure build servers.

We use the nuget restore step (v4.9.1) against the standard nuget feed & a couple of secured customer devops feeds but the restore time has gone from ~2 mins to more than 10 minute. At the outset of this the nuget restore was failing completely, allegedly due to authentication timeout. We have managed to get it working again, but taking these much longer times using the following settings:

 steps:
- task:NuGetCommand@2
   displayName:'NuGet restore'
   inputs:
     restoreSolution: src/DesktopComponents.sln
     feedsToUse: config
     nugetConfigPath: nuget.config
     disableParallelProcessing:true
     restoreDirectory:.packages

Any assistance that anyone could offer would be much appreciated. If there are any logs/settings that would be useful please let me know

Thanks in advance

Mark Middlemist