…and here’s another alternative to recover from it safely: reisub.
I would suggest you use the terminal for your updates until this condition is properly diagnosed and rectified. It is unlikely that pacman or pamac (non-gui) will be affected by such a short time-out to screen blanking; unless you’re configured to immediately hibernate instead of using a sane sleep state.
Using the terminal will make it necessary to change your workflow for a time. That shouldn’t be an issue for any experienced Linux user.
In the meantime, if you are so convinced it’s a bug with Pamac, please report it as such after first making certain it hasn’t already been reported.
Something else you could try in the meantime, however, is changing the Pamac-Manager version:
sudo pacman -Syu pamac-gtk
# or
sudo pacman -Syu pamac-gtk3
… depending which is installed.
During install you will be asked which to keep.
Lastly, failure to maintain your system (as required and expected when using a rolling release distribution) is also a recipe for unexpected conditions to arise.
- Related: System Maintenance
Check that you are fully updated, and that any issues noted in the Stable Update announcements have also been addressed; unless, of course, in the event that you’re using another branch such as ‘Unstable’.
That is all. Good luck.