Opera remembers size and position of seemingly random window among the last ones opened. Not cool.
Followed the hint about having open tabs in the window to be remembered: no consistency.

The entire pool of available thumbnails for Demon's Souls wiki:

@leocg "Choose from 2 logos or video thumbnails currently present on the page", the latter being especially useful for a page with content changing almost every day, which is the case with Twitch. Also, adding a link to speed dial and changing text name is possible within one dialogue window, but editing thumbnail to tell pages apart requires opening that specific link and then accessing a different set of settings. Auto-assigned page names were simple and sufficient for telling pages apart, and now (for quite a while "now") there's the approach of scratching one's ear by hooking the arm under a leg.

These are the links to 4 different pages (channels) within the same site, but the default names don't help telling them apart one bit. It's possible to change names shown under the tiles, but not on tiles. Page name is what should be used there, and what had been used there until about a year ago.