My issue definitely did not go away. The more I test, the more confused I get. Here are some points from me:
I've been experiencing difficulties with Vivaldi's address bar (specifically, address field) for as long as I've used Vivaldi, which is since the early beta version. The address field's functionality has never been stable for me.
There are multiple issues that may or may not be co-related, I do not even know if I am aware of all the issues that exist.
All issues are related to Address Field's suggestions drop-down.
All symptoms occur every time I use the address field, but with varying delays, from barely noticeable (~0.1 second) to ~2 seconds, until the suggestions finally stabilize; I do not know what these delays depend on; My assumption that they depend on network connectivity/lag was proven wrong; It does seem that it is directly proportionate to the size of browser's history - the larger the history, the longer the delay, but with still stochastic durations.
The issues do exist on clean new user profiles (Vivaldi Persons), but are not easily noticeable because of the above point: new profiles have empty histories, and delays are so short they can be neglected, before the address bar's suggestions stabilize.
Ironically, this issue does not seem to exist on the much less powerful Vivaldi for Android, even if its user profile is synchronised with the desktop.
More detailed steps to reproduce:
Type a single letter, choose a starting letter of a previously frequently visited domain; Example in my case: "a";
a) What happens:
Vivaldi's Address Field drop-down menu instantly spits out an initial long ordered list of suggested addresses (consisted of different address categories depending on user's settings - search history, typed history, browser history, bookmarks etc.); At this point, the address field does not receive the auto-complete (if this option is enabled in user's settings);
After a certain, always varying, time delay (~0.1 to ~2 seconds), Vivaldi's Address Field drop-down menu changes the initially suggested list; I suspect, but am not 100% sure, that only the suggested items' order is changed; There is a possibility that some items get added or removed alltogether; I also suspect that only the "Browser history" category within the suggested list gets affected, all others (typed history, search history, frequently visited etc.) seem to be fairly stable, but I also may be wrong on this; At this point, the address field will receive an auto-complete suggestion;
b) What should happen:
The suggested drop down should instantly be displayed, as is the case, but it should NOT (never, not under any circumstances whatsoever) be changed at any time from this point onwards, until the user's next action;
The address field should instantly, without any delay, receive an auto-complete suggestion, and keep it until the user's action causes it to change;
Type a second letter; Example in my case: "r";
a) What happens:
The entire cycle described under 1.a) repeats;
If the typed second letter is equal to the suggested address's second letter, the suggested auto-complete will remain;
If the typed second letter is different from the suggested address's second letter, the suggested auto-complete will disappear, and a new suggestion will occur once again, as described in the second point of 1.a);
b) What should happen:
While it is obvious that, after a suggested auto-complete appears, and the typed second letter differs from the initially suggested, Vivaldi should re-evaluate the suggestions and display both a new suggestions list and a new auto-complete suggestion, this must not happen in two steps, but only one; It should also happen either instantly, or damn close (<0.5s);
Conversely, if the typed second letter is identical to the suto-complete suggestion's second letter, the address bar's drop-down list must not change even once, let alone twice, as is the case;
For every consequent typed letter, the entire descibed cycle repeats, with two list changes per each typed letter.
I wish I could be of better assistance, but this is all I know so far. If anyone has any questions, I'll be more than happy to hear them.