Maybe try changing these values in the global.ini.php ?
; Minimum adviced memory limit in php.ini file (see memory_limit value)
minimum_memory_limit = 128
; Minimum memory limit enforced when archived via misc/cron/archive.php
minimum_memory_limit_when_archiving = 768
; Minimum adviced memory limit in php.ini file (see memory_limit value)
minimum_memory_limit = 128
; Minimum memory limit enforced when archived via misc/cron/archive.php
minimum_memory_limit_when_archiving = 768