That one might just be broken. A lot of the Odata calls simply don’t work and you have to use the custom calls. I get the same thing in my env. Unfortunately even unfiltered, I receive an empty set back, but as as soon as I filter on JobNum, it gives me the same failure. We have the customer errors toggled so we get a little more detail, so this is what we get.
JobMtlAttches is not a real table, it is created from XFileAttch data,
I think you should use custom method here to get complete Job record and take attachments from there.
For all information you probably need to write BAQ, instead of indiidual JobEntries.
Attachment information is in 2 tables: Ice.XFileAttch and Ice.XFileRef