Hi Thibault,
Thank you for contacting Syncfusion Support.
We have analyzed your query and created a workaround sample. In that sample, we did not set height property for SfAccordionItem. If we do not set the height for SfAccordionItem it automatically (Height=Auto) changes its height based on its content.
Please download the sample from below link
Link:
AccordionItemHeightTestingRegards,
Rajkumar G