Steps to reproduce:

1. Command-click the [edit source] tab on a talk page, to open the editor in a new tab.
2. The tab opens, but shows the page in Read mode.

Reloading the page (the URL will be something like https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&section=30&veaction=editsource ) doesn't open the editor. However, if you scroll to the section you want and click the [edit source] button, and wait for the editor to load, then all's well. The problem is that the whole point of opening sections in tabs is to be able to open multiple sections for quick replies, without having to wait for the editor to load or even without having to remember which sections needed replies.

This is not T165238: Source editor fails to load on direct non-view page loads where the wiki doesn't have Single Edit Tab enabled: it happens at enwiki (which is SET) as well as other wikis, and it's been going on for a couple of weeks. I've experienced this in Safari and Firefox.