Try to refer to the prev. version of SDE.

org.polarsys.chess.parent/releng/org.polarsys.chess.target.neon/org.polarsys.chess.target.neon.target

@@ -104,7 +104,7 @@
 <repository location="http://download.eclipse.org/epsilon/updates/1.4"/>
 </location>
 <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">
-<unit id="eu.fbk.tools.sde.feature.feature.group" version="0.0.0"/>
+<unit id="eu.fbk.tools.sde.feature.feature.group" version="1.0.0.202106151527"/>
 <repository location="http://es-static.fbk.eu/tools/eclipse_sde_devel"/>
 </location>
 <location includeAllPlatforms="false" includeConfigurePhase="false" includeMode="planner" includeSource="true" type="InstallableUnit">