TrueNAS cloud sync pull from OneDrive extremely slow on fast internet

Hello,
I run a single drive TrueNAS system (yes I am aware this isn’t good from a redundancy perspective, but with the price of drives right now I can only afford one), recently my single 3tb WD Red drive failed. I have replaced it with a 4tb Seagate Exos drive, I have an off-site backup stored on OneDrive that I am attempting to restore.

I created the backup using Cloud Sync tasks in TrueNAS, and never had any problems with speed. However, I am now attempting to restore these backups to the new drive, however the speed seems extremely slow. I have fast internet and get 100mbps speeds on a speedtest, however I am currently attempting to restore my Immich data backup which is 5gb. The speed starts off at about 10-15 mb/s, however it then drops to a few bytes per second. It stays like this for about 30 minutes before speeding up for about 5 and then slowing back down.

At this rate it has taken me over a day to restore 2.5gb, I need to sort this out to be able to restore the data.

Does anyone have any advice on this, or are the Rclone / Microsoft forums a better place for this.

I am running TrueNAS Scale 25.10.2.1
Many thanks in advance,
Withers99