wireguard has been moved from the packages feed to the main sources. That is the reason.
The funny thing here is that wireguard has nothing to do with the fastpath implementation.
But as gwlim's "fastpath" patches include tons of changes to things unrelated to fastpath itself, those things may break when there are external changes and the patches are not updated accordingly. (wireguard is currently at version 20171127 at both master and lede-17.01, and the gwlim 17.01 patch tries to change that to 20170629)