Rob
Ansys Employee

Looking at https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v222/en/flu_ug/flu_ug_checkpointing.html?q=checkpoint I suspect not.  If you open the Preferences (under File in Fluent) what is the I/O set as? If Legacy you'll get .cas.gz if CFF you get the h5 format. The latter is significantly faster, but can fail to write correctly.