When trying to upgrade (specifically to Moodle 3.5 but may affect other versions): we've seen cases where out-of-memory errors are encountered because the same language file seems to be pulled over and over via include() function within the load_component_strings() method. Once I switch these to include_once the problem is resolved, so my proposed solution is to change all include() calls which are inside loops in that function to include_once() which ensures that the language files are only included once - this prevents getting an out-of-memory error and allows the upgrade to finish normally.