Just to add another data point, I also experienced the second issue when trying to navigate between links with Fenix on many different occasions, including the period I was writing this post. However, I chose not to mention it because I also wasn't able to reliably reproduce it.
I used to experience this issue when I had manually configured my DNS over HTTPS (DoH) settings on Firefox for Android in about:config, and had set network.trr.mode to 3 (force DoH). Changing it to 2 (prefer DoH, use normal DNS as fallback) fixed the issue for me.
