I’ve also had issues with writing to Nemo/GVFS mounts on Mint. The solution for me was to make a standard mountpoint to a share, either through fstab or the mount command. davfs and cifs both seem to work fine. With SMB/CIFS it seems to help to declare the correct UID and GID values.
example command line for CIFS
sudo mount -t cifs -o rw,username=USER,password=PASSWORD,uid=$(id -u),gid=$(id -g) //SERVER/SHARE ~/CRYPTO/
example fstab line for WEBDAV
https://webdavserver/dav/ ~/CRYPTO davfs user,rw,noauto 0 0