I'm guessing its your LTE connection being throttled after X amount of data usage?
Its certainly not the issue here. If I use any other client (Steam, Origin etc.) to download or from anywhere else, I can download much gb's as I want and it wont slow down... as I dont have data transfer limits or anything like that on my LTE.
Only frontier launcher client have wierd this "issue", where downloading a 5gb update can take about 9 hours wich took for this case.
I started to download update 12 at about around 15.30 PM (kind of way ealier than you did) and it was not done until at 0.42 AM.
Funny and mysteriuos thing is that initial 70% was done within few mins, remain 30% of data took that much longer.
Meanwhile, I was able to download from steam a 28 gb game and install it without any problems, and it was done within about 35 mins (while elite was still updating).
Thats about 6 times much as data downloaded at 35min vs 5.5 gb update for elite wich took over 9 hours...
I have no idea whats going on with frontier servers, but is clearly something very wrong on thier end, not mine(I guess I am on their blacklist or something), where download speed was wierdly capped at 0.03 mb/s after certain point, and it would sometimes go up to like only up to 2-3 mb/s for min or two, only to be back at 0.03 mb/s. Again, before I hit that 70% mark, download speed was at 20 to 30 mb/s.
Its not first time I had issue with downloading a update using frontier launcher, but that oddy update 12 was so far worst of worst I had so far.
And Ive been dealing with this launcher since launch of elite at 2014, and few years ago, it worked much, much more better.