When 'frontend' directory is moved, then Designer can not handle Lit component within Lit component.
NOTE: Designer does not have same problem with Polymer components.

Steps to reproduce

My sample project:
skeleton-starter-flow-spring-frontend-moved.zip

1. Clone vaadin 14 starter project

   git clone https://github.com/vaadin/skeleton-starter-flow-spring.git
   cd skeleton-starter-flow-spring
   git checkout v14

2. Rename 'frontend' direcotry to 'frontend-moved'

   git mv frontend frontend-moved

3. Change frontend directory. Edit maven project file 'pom.xml'.
   Add 'frontendDirectory' -configuration

   <configuration>
       <frontendDirectory>${project.basedir}/frontend-moved</frontendDirectory>
   </configuration>
   

   Into 'vaadin-maven-plugin' in 'plugin' section.
   NOTE: The 'vaadin-maven-plugin' is in two sections 'build' and 'profiles'.
   End result sample:

       <plugin>
           <groupId>com.vaadin</groupId>
           <artifactId>vaadin-maven-plugin</artifactId>
           <version>${vaadin.version}</version>
           <configuration>
               <frontendDirectory>${project.basedir}/frontend-moved</frontendDirectory>
           </configuration>
       </plugin>
   

4. Import into Eclipse IDE
5. Create new Lit component 'lit-test-child'
6. Create new Lit component 'lit-test-parent'
7. Drag&Drop 'lit-test-child' into 'lit-test-parent'

Actual behavior

Designer does not show any content for child Lit component.

If "lit-test-parent" is reopened, then just white canvas is shown.
No content at all :(

Expected behavior

Designer should show 'lit-test-child' componet content within the 'lit-test-parent' component view.

IDE, Designer and OS version