Both $PAGE->set_title() and $PAGE->set_heading() already process the contents passed with format_string(). So any call of this type:

• $PAGE->set_title(format_string(… (there are 42 of this, at least)
• $PAGE->set_heading(format_string(… (there are 25 of this, at least)

Context in format_string() calls is only needed if it does not match current $PAGE->context OR if it has not been set. And any of these operations set it:

• require_login() calls passing the 3rd, $cm parameter.
• $PAGE->set_cm() calls.
• $PAGE->set_context() explicit calls.

This is about to search and destroy all those incorrect uses, looking to each carefully, ensuring that context is always set.