Very happy with the extension for a long time. Great job !:)
I have many tabs always open and with a well defined order. But since a few weeks ago, every time I start Opera, the order of several tabs changes arbitrarily and the cause is this extension
It's making me crazy. I hope it can be fixed quickly because I'm already thinking to move to another browser

Don't use this extension for anything you just described. Use this one instead: https://addons.opera.com/en/extensions/details/classic-tabs/ It has the same main features, plus delay options to fix those bugs. Its "Options" page/settings explain everything.

The only thing you should use SimpleTabOrder for is its "Event Page" feature.

I hope this gets fixed, cause this extension does something important to me! This extension does something people have complained about opera for quite a while too!

I have reproduced the same problem with this extension in other browsers. In the end, leaving the option "On tab open" --> "Position" on "follow default behaviour" stops the issue.
For the "position right of current tab", in Opera, you have to use another extension combined with this one.
Right now I'm using Brave as my main browser and the problem is solved (you can try also Vivaldi, in this case you don't need this extension because Vivaldi have a lot of Tab options).

I hope this gets fixed, cause this extension does something important to me! This extension does something people have complained about opera for quite a while too!