You don’t need to download huge amounts to test the line with AA; and it would bankrupt you. AA continually tests the line every few seconds; measures the latency and checks for packet loss: See https://support.aa.net.uk/CQM_Graphs You get pretty pictures that show you the line performance minute by minute and also show your traffic usage.
His issue is his PPP session terminates when he does large file transfers.
He needs to run large file downloads to replicate the issue.
Uno run practically identical line monitoring to AAISP.
An example of this from Bangers line is attached.
I actually prefer how Uno display the data.
It's just a Broadband Quality monitor which you can setup for free on ThinkBroadband, who use a FireBrick FB6000 series ping box like AAISP.
Going by the TBB thread Uno have progressed the ticket within a few hours.
Matt himself is keeping an eye on the ticket and I'm sure they'll get to the bottom of it.
The answer isn't always switch to AAISP.
Their cost for what is a metered service is ridiculously expensive particularly for those who consume large amounts of data.
Banger would use over 37.5% of their largest monthly quota running his hourly tests alone.
Uno are a good ISP and given the proper time to investigate the issue will likely get to the bottom of it.