Here to report that I am also experiencing the same issue, rotating from portrait to landscape looks as if all the portrait-oriented sites are next to each other. And since they have a smaller width I see a few tabs as if “to the left” of my current one. Also happens on the start page as already mentioned.
Also mentioned, opening a new tab while in landscape mode and loading a website works properly. The issue happens when rotating portrait to landscape.
App version: 1.3.22 (3) (WebKit 8615.3.12.10.2)
System version: 16.6.0
Device type: iPhone SE 2nd gen
Native bounds: (750.0, 1334.0)
Scale: 2.0