after following the guide:
https://matomo.org/docs/tag-manager/#advanced-variables-settings-default-value-lookup-table

most of the times (but not always, could it be a race condition?) I end up with a request to matomo that doesn't contain an idSite in the request:
...&idsite=&...

weirdly enough it's happening only during EEcomerce calls

_paq.push(['addEcommerceItem', '999', 'foo, 'bar', 999, 1]);
_paq.push(['trackEcommerceOrder', '999999', 99]);

Matomo version: 3.13.2