Whilst this probably only applies to a handful of users now, I have run into this issue updating 2 x 64GB Jolla tablets from 3.4.0.24 to 4.0.1.48

It goes without saying that you have enough space for the install and can only recommend using sfos--upgrade from Open Repos https://openrepos.net/content/olf/sfos-upgrade as I am sure that all aware there is no installation progress bar if using UI and device must not be switched off inadvertently before update complete.

Problem that arises is that on first device it re-booted into 4.0.1.48 (without WLAN being active) and made mistake of carrying out "Restart" and it then "hung" upon Jolla Intel inside screen and upon second device on reboot after installation "hung" upon Jolla Intel inside screen. In both cases after leaving for decent interval >30 mins had to make decision to power them down wondering whether they would be "bricked".

The solution in both cases was to use Jolla Recovery Mode > Option 2 (Reboot device). https://jolla.zendesk.com/hc/en-us/a...Recovery-Mode-

I only had this problem when updating from 4.0.1.45 (EA) to 4.0.1.48 (EA) but waiting a while and a simple manual reboot (long-press the On/off button) did the job. It is now running fine without any recovery (although I thought initially I would need a recovery)

Mine also hung at the Jolla logo after update from 3.4.
I entered recovery and did "filesystem recovery (or check?)" just for the chance and all works since then.
Now reading it would have been sufficient to just enter recovery is something i did not try, but good to know.