Sony explains FS5 firmware withdrawal - seems it's a minor issue

FS5 firmware clarification

Sony's sudden withdrawal of the latest FS5 firmware has taken users by surprise. The explanation, it seems, is simple: it's a minor, relatively obscure issue.

 Sony's latest software release for their PXW-FS5 (firmware v. 4.0) and PXW-Z150 (firmware v. 2.0) cameras has been withdrawn, to the surprise of users. We spoke to Sony USA and it has sent us this statement:

In response to instances of firmware issues for the PXW-FS5 (v. 4.0) and PXW-Z150 (v. 2.0), Sony has to date confirmed that these issues only occur in specific applications of HLG in HD shooting modes. We are continuing to investigate further and are working to release a firmware update in the coming weeks. We appreciate our customers’ understanding.

So, really, there's nothing to see here. This is clearly a niche issue with HDR aquisition. Sounds like if you've already upgraded you're not going to have a problem unless you delve into HDR. And a fix is on its way. 

Thanks to Sony for their quick response to our question.