Since [1], an attribute is added on all snippet contents, on the main node, to be able to identify them and better support them. This is added thanks to the t-snippet or the t-snippet-call instruction. The problem was this was not working if the first node of the snippet definition is also a t-call to another sub template. This now works. [1]: https://github.com/odoo/odoo/commit/11c60739e4f4379a61581ed179bc7debbb5e91f9 task-2276740 PR #53175