First of all, thank you for all of your replies!
As you have pointed out the probability of a network problem, I don't think that is the problem, I've got 9 other ASIC miners and 11 GPU mining rig on the network, all running fine for months now. Nevertheless, I have tried pinging the server, and it does work!
As BitMaxz suggested, I did a physical reset on the miner, actually had to do all 3 of them which resulted in the following:
1.The miner restarted and was showing the expected hashrate for mining with the default settings, and it had a Hardware Version and BMminer version as well.
2.When changing the settings to my own, it wasn't mining for 30-40 minutes
3.After hard resetting again, changing the settings it DID mine for me for like 10-15 minutes, it restarted a couple of times and now won't do anything without my restart-input and the Hardware and BMminer version are blank again.
The miner still doesn't allow me to upgrade the software, still showing the "413 Request Entity Too Large" problem. My S9 has an SD slot though, so i might need to try boot from there/flash from there?
One more thing, I have tried the setup with a new PSU now, and that did not help unfortunately.
https://imgur.com/0RNNpRShttps://imgur.com/Wrv394MI would like to thank you guys for helping me!