While running an SE to ESE conversion, the following error presents and the conversion fails.
Neither a Quick IntegrityCheck nor a Full IntegrityCheck with fixes solves the problem.
This is an edge case specific to legacy backup indexes and is usually due to a plugin that was used. A known case where this can happen is when a Linux filesystem (case sensitive) was backed up from a Windows environment (case insensitive).
The following steps may resolve the problem.
1. Obtain the relevant account's encryption key and make a dump of the backup indexes before and after conversion (before an IntegrityCheck deletes the converted indexes)
2. Compare the index dumps to determine which files will be lost in conversion. If the files that are to be lost are insignificant, the verification step can be skipped to allow the conversion to pass without verification. This will require entering a setting in the account's LocalSettings file to prevent the IntegrityCheck from running for some time, allowing the converted indexes to remain.
Please contact Support if you need assistance.