FYI: I had problems with linux-image-4.19.0-5-amd64, too, esp. on writing large amounts of data to an USB block device (USB-C). "sync" got stuck, umount didn't work, host became unresponsive, etc. Reset necessary. linux-image-4.19.0-6-amd64 (in proposed-updates) seems to work better. Regards Harri