Netflix Won't Stream At More Than 720p

I'm having problems watching Netflix at anything higher than 720p in the evening. During the day it works at 4K without any problems, but past 7pm it is impossible. I ran into this guide - https://www.comparetv.com.au/how-to/how-to-troubleshoot-network-connection-issues-on-netflix/ and tried everything from it, no luck.
Then I contacted my ISP (it is Telstra, I have an NBN L package which is more than enough to cover my needs, with boost enabled) and they told me that everything is in order with my line. Speedtest shows 40 - 50 Mbps, depending on the time I do the measurement, but that should still be enough.
Anyone got any ideas what could cause this problem and how to get it fixed since I hate it that I can't enjoy my Acer Predator in the evening :/

 

Hi Laura,

Sorry for taking my time to respond . Thank you very much for this extensive answer. I've read everything and, well, yes, my ISP is 99% to be blamed given all the data I've gathered on my end. Luckly though I'm nearing the end of the contract and won't be renewing it, that is for sure.

 

Do not trust your internet speed from the "speed test" applications, reason being..... I have a 25mbs speed on the "speed test" but in reality and, using an "internet download manager" all I get tops is 2.5 mbs. I have spent months contacting Telstra with drop outs (six in an hour) and just recently I was given a 5G connection but still the same of 2.5 mbs max. Telstra is not the only one, on whirlpool forums almost all are under the advertised speed. Regards informe

 

Well is seems your ISP Telstra could be throttling you.Have you been watching to many things or downloading to much in the last few weeks.

If so this could be your problem.

 

Why do people keep bringing up year old threads.