In SfAccordion, When loading Label as direct children of Header or Content of AccordionItem, then it will lead to exception in Xamarin.Forms 4.0 and above version.
However, the issue can be resolved in application level by loading Label inside Grid in AccordionItem.Header and AccordionItem.Content.
You can also refer the following article.
XAML
Loading Label inside Header and Content in Grid
<ContentPage xmlns="http:https://xamarin.com/schemas/2014/forms"
xmlns:x="http:https://schemas.microsoft.com/winfx/2009/xaml"
xmlns:syncfusion="clr-namespace:Syncfusion.XForms.Accordion;assembly=Syncfusion.Expander.XForms"
x:Class="AccordionXamarin.MainPage" Padding="{OnPlatform iOS='0,40,0,0'}">
<ContentPage.Content>
<syncfusion:SfAccordion ExpandMode="MultipleOrNone" >
<syncfusion:SfAccordion.Items>
<syncfusion:AccordionItem>
<syncfusion:AccordionItem.Header>
<Grid>
<Label Text="Cheese burger" HeightRequest="50" VerticalTextAlignment="Center"/>
</Grid>
</syncfusion:AccordionItem.Header>
<syncfusion:AccordionItem.Content>
<Grid Padding="10" BackgroundColor="NavajoWhite">
<Label Text="Hamburger accompanied with melted cheese. The term itself is a portmanteau of the words cheese and hamburger. The cheese is usually sliced, then added a short time before the hamburger finishes cooking to allow it to melt." VerticalTextAlignment="Center"/>
</Grid>
</syncfusion:AccordionItem.Content>
</syncfusion:AccordionItem>
<syncfusion:AccordionItem>
<syncfusion:AccordionItem.Header>
<Grid>
<Label Text="Veggie burger" HeightRequest="50" VerticalTextAlignment="Center"/>
</Grid>
</syncfusion:AccordionItem.Header>
<syncfusion:AccordionItem.Content>
<Grid Padding="10" BackgroundColor="NavajoWhite">
<Label Text="Veggie burger, garden burger, or tofu burger uses a meat analogue, a meat substitute such as tofu, textured vegetable protein, seitan (wheat gluten), Quorn, beans, grains or an assortment of vegetables, which are ground up and formed into patties." VerticalTextAlignment="Center"/>
</Grid>
</syncfusion:AccordionItem.Content>
</syncfusion:AccordionItem>
...
</syncfusion:SfAccordion.Items>
</syncfusion:SfAccordion>
</ContentPage.Content>
</ContentPage>