Nope, I haven't seen that error before.
Try to do a "save as" and redirect the download to a target folder on your desktop.
As to the download times, look very carefully at the AM and PM designations in your history graph. It is useless due to the many errors:
I suspect that the actual real accuracy of any of the data usage numbers that HN puts out as quite precise are in actuality very very UN-precise, and based on something other than an actual way to really measure how much internet band with I am actually really using. But i have no way of realy actually knowing that
Measuring usage on a Sat connection is not as simple as one would think.
The only way to take a stab at it is to run something like Glasswire and use it in conjunction with a before and after of the dashboards "at a glance" usage meter.
Some files you may download may be able to be compressed for transmission. As an example a file may be 50 MB in size, can be compressed to 30 MB for transmission purposes. Your usage (as measured by the "At A Glance" meter) will only be "charged" the 30 MB.
In other areas there is "command and control" data bytes that will not be charged against your usage allowance..
There is a lot "manipulation" of your data as it goes through the modem>>>sat>>>>gateway "loop".