Under certain circumstances it is possible that fetching cache files from DFS will fail.
While this is an expected situation (caused by network/NFS issues, for example), the generated error message is some cases is incoherent:

eZDFSFileHandlerMySQLiBackend::_fetch:

Size (73672) of written data for file 'var/.../cache/user-info/2/9/7/0/231/user-data-2970231.cache23757-978305412tmp.php' does not match expected size 73672

The problem is that the local file size is checked against the dfs file size, and the error message displays the local file size and metadata size.

Steps to reproduce:

This has occurred in live environment and appears to be impractical to reproduce on a test env.
It is possible/likely that either the dfs file size or metadata changes while the _fetch() method is being executed.

Other info:

Ref: https://github.com/ezsystems/ezpublish-legacy/blob/master/kernel/private/classes/clusterfilehandlers/dfsbackends/mysqli.php#L718

Suggested course of action would be to either fix the error message, or
reload the dfs filesize / metadata size if both mismatch.