Yes deffo sounds like boost cut or plug gaps

there are several reasons.

its colder at night so makes more boost which can push it over the limit, its prob running
at the limit...

plug gaps set too wide, and its blowing out the spark

plugs not up to the job, breaking down under the heat.

but usually is it goes ok under normal excelleration, then its probthe boost.

dont disconnect the amal valve as the engine needs it to regualte the boost.
i might over boost run lean and melt a piston, then GAME OVER !!!

what stage of tune is it ??