ExecutionEntity#restoreProcessInstance is not safe when parts of the execution tree are removed in parallel. For example, consider https://github.com/camunda/camunda-bpm-platform/blob/7.4.0/engine/src/main/java/org/camunda/bpm/engine/impl/persistence/entity/ExecutionEntity.java#L1129-L1140. The parentId may be not null but the parent may already be deleted when it is fetched, resulting in a NullPointerException.

Checkthe entire method for more possible occurrences of this problem and fix them.