When connected via ssh or rpi-connect from a remote computer and then it can happen during and due to the update that the connection closes and this can stop the update.

To avoid this, use the program screen (install it with sudo apt install screen). It creates a local terminal (screen session) using screen -S <name>, Commands can then be run and detach with Ctrl+a followed by d. So remote connection loss will not stop the running program. screen -ls shows the sessions and session ID's and later on re-attach screen -r or screen -r <session ID>

Ctrl+a ? gives help