Drag the folder(s) you want to rescan, from windows explorer into the lib. window. Then click library button / remove missing files...
Or... the opposite way, drag the biiiig main static library folder into the lib.window, end then remove it from watch folders, so only the other (small frequently changing) will be scanned with rescan. To rescan the Biiiig one, drag it into lib.again.(+remove missing files)
*sigh (still) under construction*