Change in the structure template expansion
Org 9.2 comes with a new template expansion mechanism, combining
org-insert-structure-template bound to C-c C-,.
If you customized the org-structure-template-alist option manually, you probably need to udpate it, see the docstring for accepted values.
If you prefer using previous patterns, e.g. <s, you can activate them again by requiring Org Tempo library:
or add it to org-modules.
If you need complex templates, look at the tempo-define-template function or at solutions like Yasnippet.
None of the new options work any better or provide any more value than the old one. Forgot about finding out why the change was made. They do require me to redo 20 customized options, a task I do not relish.
My frustration is in the lack of transparency behind the change. I follow the org-mode mailing list and I not only missed the whole thing but can’t find the genesis.