You may try a GNOME shell extension as a workaround called Keep awake!
Keep your computer awake! Forbid your computer to activate sceensaver, turn off the screen or suspend when it is idle for a while. Toogle [sic] this option on or off with one click.
Once you install this extension you'll see an "eye" icon in your top bar.
(screenshot source: extension's homepage at extensions.gnome.org)
Clicking on the eye will switch between "normal" and "no screen-lock or suspend" mode.
Another advanced extension which does the same but provides more customisability is Caffeine.
Warning: There is (or was, not sure whether it's fixed already) a bug in Caffeine which may freeze your computer for ~30 seconds after clicking on the power-off button in the status menu.