Welcome to this user forum.
I have moved your post to this new thread, so you can get personal help from the community or moderators, so please watch this thread for updates.
What program are you using to upload the files?
What upload speed do you get when you run the BT Wholesale speed tester?
Its was probably internal memory fragmentation in the home hub input buffer.
Its best to limit the upload speed on the Google program, so that you do not exceed the upload speed for your connection, that should avoid any buffer overflow, and a crash.
A limit of 2MB (thats megaBYTES) a second would be an upper limit for your connection. On the Google program, that equates to 2000KB on the preference - settings - nework settings screen.