diff --git a/app/src/main/java/org/tasks/sync/microsoft/MicrosoftConverter.kt b/app/src/main/java/org/tasks/sync/microsoft/MicrosoftConverter.kt
index e725db88e..0782133ff 100644
--- a/app/src/main/java/org/tasks/sync/microsoft/MicrosoftConverter.kt
+++ b/app/src/main/java/org/tasks/sync/microsoft/MicrosoftConverter.kt
@@ -25,14 +25,15 @@ object MicrosoftConverter {
 
     fun Task.applySubtask(
         parent: Long,
+        parentCompletionDate: Long,
         checklistItem: Tasks.Task.ChecklistItem,
     ) {
         this.parent = parent
         title = checklistItem.displayName
         completionDate = if (checklistItem.isChecked) {
-            checklistItem.checkedDateTime?.parseDateTime() ?: System.currentTimeMillis()
+            checklistItem.checkedDateTime.parseDateTime()
         } else {
-            0L
+            parentCompletionDate
         }
         creationDate = checklistItem.createdDateTime.parseDateTime()
     }
@@ -120,7 +121,7 @@ object MicrosoftConverter {
             } else {
                 Tasks.Task.Status.notStarted
             },
-            categories = tags.map { it.name!! }.takeIf { it.isNotEmpty() },
+            categories = tags.map { it.name!! }.takeIf { it.isNotEmpty() } ?: emptyList(),
             dueDateTime = if (hasDueDate()) {
                 Tasks.Task.DateTime(
                         dateTime = DateTime(dueDate).startOfDay().toString(DATE_TIME_FORMAT),
diff --git a/app/src/main/java/org/tasks/sync/microsoft/MicrosoftSynchronizer.kt b/app/src/main/java/org/tasks/sync/microsoft/MicrosoftSynchronizer.kt
index 481e3d6e8..7c2026921 100644
--- a/app/src/main/java/org/tasks/sync/microsoft/MicrosoftSynchronizer.kt
+++ b/app/src/main/java/org/tasks/sync/microsoft/MicrosoftSynchronizer.kt
@@ -11,15 +11,14 @@ import dagger.hilt.android.qualifiers.ApplicationContext
 import io.ktor.client.call.body
 import io.ktor.http.isSuccess
 import kotlinx.serialization.json.Json
-import org.tasks.broadcast.RefreshBroadcaster
 import org.tasks.Strings.isNullOrEmpty
 import org.tasks.analytics.Firebase
+import org.tasks.broadcast.RefreshBroadcaster
 import org.tasks.caldav.VtodoCache
 import org.tasks.data.dao.CaldavDao
 import org.tasks.data.dao.TagDao
 import org.tasks.data.dao.TagDataDao
 import org.tasks.data.entity.CaldavAccount
-import org.tasks.data.entity.CaldavAccount.Companion.ERROR_UNAUTHORIZED
 import org.tasks.data.entity.CaldavCalendar
 import org.tasks.data.entity.CaldavCalendar.Companion.ACCESS_OWNER
 import org.tasks.data.entity.CaldavCalendar.Companion.ACCESS_READ_WRITE
@@ -403,6 +402,7 @@ class MicrosoftSynchronizer @Inject constructor(
                 list = list,
                 parentId = task.id,
                 parentRemoteId = caldavTask.remoteId!!,
+                parentCompletionDate = task.completionDate,
                 checklistItems = it,
             )
         }
@@ -421,6 +421,7 @@ class MicrosoftSynchronizer @Inject constructor(
         list: CaldavCalendar,
         parentId: Long,
         parentRemoteId: String,
+        parentCompletionDate: Long,
         checklistItems: List<Tasks.Task.ChecklistItem>,
     ) {
         val existingSubtasks: List<CaldavTask> = taskDao.getChildren(parentId).let { caldavDao.getTasks(it) }
@@ -451,6 +452,7 @@ class MicrosoftSynchronizer @Inject constructor(
             } else {
                 task.applySubtask(
                     parent = parentId,
+                    parentCompletionDate = parentCompletionDate,
                     checklistItem = item,
                 )
             }
diff --git a/app/src/main/java/org/tasks/sync/microsoft/Tasks.kt b/app/src/main/java/org/tasks/sync/microsoft/Tasks.kt
index d079ae3e7..55873f69c 100644
--- a/app/src/main/java/org/tasks/sync/microsoft/Tasks.kt
+++ b/app/src/main/java/org/tasks/sync/microsoft/Tasks.kt
@@ -22,7 +22,7 @@ data class Tasks(
         @EncodeDefault val body: Body? = null,
         @EncodeDefault val importance: Importance = Importance.low,
         @EncodeDefault val status: Status = Status.notStarted,
-        @EncodeDefault val categories: List<String>? = null,
+        val categories: List<String>? = null,
         val isReminderOn: Boolean = false,
         val createdDateTime: String? = null,
         val lastModifiedDateTime: String? = null,
@@ -31,7 +31,7 @@ data class Tasks(
         val linkedResources: List<LinkedResource>? = null,
         @EncodeDefault val recurrence: Recurrence? = null,
         @EncodeDefault val reminderDateTime: DateTime? = null,
-        @EncodeDefault val checklistItems: List<ChecklistItem>? = null,
+        val checklistItems: List<ChecklistItem>? = null,
         @SerialName("@removed") val removed: Removed? = null,
     ) {
         @Serializable