UPDATE: Problem caused by other module. Not a toolbar menu bug.
Nested menus do not work for users other than user ID 1. The top level is rendered, but sub levels are not visible.
In the JS console I do see an HTTP 403-forbidden error for path /toolbar/subtrees/undefined?_wrapper_format=drupal_ajax. I can certainly exclude any misconfiguration regarding roles/permissions: The menu itself is visible for the user, the top level entry is visible, but sub entries are invisible even for external URLs or anonymously-allowed routes.
I tried adding sub entries through menu UI and by my_module.links.yml, same error in both cases.
Adding/removing the "expanded" checkbox in menu UI does not change anything.
Adding setMaxDepth(4) in toolbar_menu_prerender_toolbar_tray as suggested in
issue #2945706 →
did not fix the problem.
Closed: cannot reproduce
2.1
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
@hudri Thank you for figuring this out and providing a fix. We were experiencing the exact same error and I couldn't figure out why until I found this bug report and discovered we were also unsetting the administration menu just like you were in order to hide it from certain users. Your fix works perfectly!