Logs of SkippedItem Failure during Migration From GWS Gmail to M365 Exchange Online

Hello,

I have recently completed migration from GWS Gmail to M365 Exchange Online utilizing Migration Batch microsoft provided.

Some of items, However, were skipped during the migration.

With Powershell Command as below, I found 6 failure errors in common.

$ustats=Get-MigrationUserStatistics "UPN" -IncludeSkippedItems -IncludeReport -DiagnosticInfo "Verbose"

$ustats.Report.BadItems | FT folder,subject,failure

Could anyone of you let me know of the reasons behind below SkippedItem Failure Logs?

There is no such docs to give me answers for that.

1.ConversionFailedException: The message content has become corrupted. --> Decoding of header Subject failed; raw value: --> Character set name (5601) is invalid or not installed.

2. GoogleEventRecurrenceException: Error occurred while converting iCal recurrence to XSO recurrence. RRULE: 'Start.Date="" . Error : 'Invalid ICAL element: RRULE.InvalidRecurrenceUntil'

3. GoogleEventIgnoredTombstoneInstanceOrphanException: Ignored a tombstone of an instance of a series in which the user does not have access to the entire series.

4. MessageSubmissionExceededException: Cannot save changes made to an item to store. --> MapiExceptionMaxSubmissionExceeded: Unable to save changes.

5. UnsupportedGmailFilterComponentException: Unsupported Gmail filter criteria or action.

6. UnsupportedGmailFilterExpressionException: Unsupported Gmail filter expression.

Thank you in advance!