Cannot Connect to Tidal anymore

Hi,
I posted elsewhere, but I’m now getting the exact same error. The ROCK is detected all well and good, but I can never get past the panel where I enter my credentials

It’s not my credentials that are the issue, since I get an error if I type them wrong. After about a half minute of waiting I get the following error:

My core doesn’t get detected on my either my phone or my partner’s phone.

I’ve tried everything so far, including a fresh reinstall of Roon Rock after wipping the hard drive clean and I’ve reset my modem twice, once to factory settings. What’s puzzling is that I haven’t changed anything in my setup to get that issue. After reinstalling Roon Rock, I got prompted for a software update on my computer and the ROCK, which seem to have worked fine.

It appears in my modem’s control panel just fine, with the right IP, I can connect to the ROCK by typing in the IP, and I can access the hard drive from my PC. I was advised to change my DNS settings, but it’s unclear to me what to do exactly. Plus, in my modem, the DNS settings are locked. My router is not listed in your troubleshooting list, and without any further assistance on the DNS issue, if that is indeed the cause, I’m out of ideas. I’ve now wasted about a whole day reinstalling things and trying to apply smaller changes based on what I could google and I’m gradually not finding it worthwhile anymore. I haven’t been able to use Roon for over a week and half now.