Kindly note that this is applicable only for agents under a Distribution Server and is not supported for Roaming Agents in Cloud version.
Sometimes, patches can't be downloaded due to some issue in the session keys and hash keys of the download link. In such cases, you can manually download the patch and upload it to the patch store directly from console using upload patches option.
Follow the steps given below to resolve this issue:
If you have changed the location of the patch store, then navigate to the path mentioned in the registry value which has been highlighted in the screenshot below:
DesktopCentral -> DCDistributionServer -> PatchStore_Directory

If the issue persists even after following the above-mentioned resolutions, please feel free to contact support.