MailboxExportRequest Fails / UnableToReadPSTFolderPermanentException

I am attempting to create a PST file for a very large mailbox (about 90GB).

Created it using:

New-MailboxExportRequest -Mailbox mailboxname -FilePath \\server\d$\Backup\mailbox.pst -BadItemLimit 200 -AcceptLargeDataLoss

It starts running, has created a file that's about 70GB, and then fails.

Getting the RequestStatistics report, I see:

FailureCode                            : -2146233088
FailureType                            : UnableToReadPSTFolderPermanentException
FailureSide                            : Target
Message                                : Error: Unable to read folder ID '33154'. Check the PST file for possible 
                                         corruption. --> Heap id type does not match

The end of the log file looks like this:

                                         4/6/2018 12:13:04 PM [SERVER] Fatal error 
                                         UnableToReadPSTFolderPermanentException has occurred.

I've tried it over a few times and same error.  What would be next steps here?