To test the reporting engine on Odoo #V17 and #V18, I tried the creation of a QWeb-based PDF report, to see if I can change some parameters to get past the problem of the error : "UserError odoo.exceptions.UserError #Wkhtmltopdf failed (error code : -10)" described in this link, I have this behavior from the report :

• The QWeb template with "<t t-call="web.external_layout">" : the report is printed without error.
• The QWeb template with "<t t-call="web.internal_layout">" : the report throws the described error.

So for the same configuration of Odoo 17 and 18, the reporting engine behaves differently, when changing the layout of the report from web.internal_layout --> web.external_layout?!. 

Is this a bug or a misconfiguration or what, can please someone help me to understand ?!