Hey! I think I've found a solution to this problem.
I'm sure you've done your fair share of scouring the internet for solutions, but like me didn't have any luck finding a proper solution. I decided to go tinkering around in the settings for the app - I'm using the CurseForge launcher now, though I imagine at the time of writing you were using Twitch. Obviously they're transitioning over to CurseForge, so I'll proceed with what I did for this.
First off, I went into the settings of the app - little cog in the bottom left corner - and went to Addons. There's a little slider for Backup Space, which I bumped all the way up to the maximum it would let me, 10MB.
Then, I went to download the modpack. It got further than it was normally - typically it was stopping at mod 101 of 181, which was a pretty big one, but this time it got somewhere around 150 before it gave me the error again. That was frustrating.
I tried downloading it again, but this time while it was downloading, I did not do anything else in the background. No YouTube videos, no Discord chats, nothing that would use up broadband. I just let CurseForge download and install the modpack. This time it worked.
Tl;dr: Go to settings, addons, set backup space to max. Go to download your modpack and don't do anything else online while it's downloading.
Hope this helps!