Are the files you watching in /mnt/c/ or inside of the WSL filesystem?
I can’t say I came across any issues with watching files. The only hiccup I experienced was BrowserSync needing me to specify firefox.exe or chrome.exe including the *.exe extension as well as assuring my /etc/hosts and /mnt/c/Windows/System32/drivers/etc/hosts were synced (i.e. cat /mnt/c/Windows/System32/drivers/etc/hosts | grep 192.* | sudo tee -a /etc/hosts).
I committed everything, overwrited everything with files from master from sage9 repository and then selectively reverted/committed to keep customizations. Afterwards it seems to work now.