I have the same issue when running the test with Firefox. I've used Firefox for years and the current version is Firefox 90.0.2 (64-bit). I've also run the test with Microsoft Edge, Opera and Brave browsers with no problems, so it appears there is some kind of conflict with the Firefox browser. Perhaps something to do with EOF marker?
When testing upload at 2Mb it locks up between 40% +- 5%, but I've tried using manual size and anything 1Mb or higher will not complete with Firefox.
Starting with manual size 256kb, it blazes through that and adjust size to 1.3MB and never gets above 0% nor produces any error message.
Starting with manual size 512kb, it blazes through that and adjust size to 2.4MB and stalls out at 50%-55%, then say "something went wrong..." about a minute later.
Starting with manual size 1MB, it never gets above 0% nor produces any error message.
Starting with manual size 1.5MB, it never gets above 0% nor produces any error message.
Starting with manual size 3MB, it it stalls at the 45% +- 5%.
Starting with manual size 6MB, it it stalls at the 75% +- 5%.
Starting with manual size 12MB, it it stalls at the 87% +- 2%.
Starting with manual size 25MB, it it stalls at the 93% +- 2%.
Starting with manual size 50MB, it it stalls at the 95% +- 2%.
Starting with manual size 75MB, it it stalls at the 98%
