According to the latest p4v documentation (https://www.perforce.com/perforce/doc.current/manuals/p4v/p4v.pdf) I should be able to unload a task stream from p4v by right clicking the stream and selecting unload. This option never appears for me. Is there some condition that must be met for this option to appear? Thanks!
Edit: I am running p4v 2018.2/1687764
You don't mention what version of P4V you're using, but as a general rule, if functionality described in the latest version of the documentation doesn't match what you see in the product, make sure you're running the latest version of the product.
If you're running the latest version of the product, try performing the analogous operation from the command line (p4 unload). If you get an error message, that'll be a strong clue as to why you can't do it from P4V.