A programme of flood defence work along Broadland rivers is responsible for some path closures. It seems fairly long-term as they've gone to the trouble of printing this message on the OS map! I've also now seen a message on Norfolk County Council's website.
walking the second half of the Weavers' Way I'd not seen any of these messages and this first notice just outside Yarmouth was a heart-sinking moment. The poster says "Not possible to provide a diversion" and suggests catching the train from Yarmouth to the Berney Arms.
According to the contractor's website, we're now half-way through a 20-year scheme. The point is to improve access as well as to reduce the flood risk, so we can look forward to great paths, but also some inconvenience for quite a while to come.
Note that this work affects the section of Weavers' Way between Potter Heigham and Great Yarmouth. The first half of the long-distance path is I believe unaffected.